Bug 1717983 - Don't consider a browser active if the tab is inactive but we're preserving layers. r=nika

GeckoView always calls preserveLayers(true) on all <browser> elements,
which causes the puppet widget to always be considered visible.

Given how the code worked before, aBrowsingContext.isActive = false
after that call would deactivate the pres shell, but after my patch it
stops doing so.

We don't really want to un-throttle the refresh driver etc just because
we're preserving layers, so propagate the state to the child process and
account for that in the logic to determine PresShell activeness.

Depends on D118703

Differential Revision: https://phabricator.services.mozilla.com/D118884

dom/ipc/BrowserChild.cpp

@@ -341,6 +341,7 @@ BrowserChild::BrowserChild(ContentChild* aManager, const TabId& aTabId,
 #endif
       mShouldSendWebProgressEventsToParent(false),
       mRenderLayers(true),
+      mIsPreservingLayers(false),
       mPendingDocShellIsActive(false),
       mPendingDocShellReceivedMessage(false),
       mPendingRenderLayers(false),
@@ -2960,21 +2961,7 @@ void BrowserChild::MakeVisible() {
     mPuppetWidget->Show(true);
   }
 
-  if (nsCOMPtr<nsIDocShell> docShell = do_GetInterface(WebNavigation())) {
-    // The browser / tab-switcher is responsible of fixing the browsingContext
-    // state up explicitly via SetDocShellIsActive, which propagates to children
-    // automatically.
-    //
-    // We need it not to be observable, as this used via RecvRenderLayers and co.,
-    // for stuff like async tab warming.
-    //
-    // We don't want to go through the docshell because we don't want to change
-    // the visibility state of the document, which has side effects like firing
-    // events to content, unblocking media playback, unthrottling timeouts...
-    if (RefPtr<PresShell> presShell = docShell->GetPresShell()) {
-      presShell->ActivenessMaybeChanged();
-    }
-  }
+  PresShellActivenessMaybeChanged();
 }
 
 void BrowserChild::MakeHidden() {
@@ -2994,15 +2981,36 @@ void BrowserChild::MakeHidden() {
     mPuppetWidget->Show(false);
   }
 
-  if (nsCOMPtr<nsIDocShell> docShell = do_GetInterface(WebNavigation())) {
-    // We don't use BrowserChildBase::GetPresShell() here because that would
-    // create a content viewer if one doesn't exist yet. Creating a content
-    // viewer can cause JS to run, which we want to avoid.
-    // nsIDocShell::GetPresShell returns null if no content viewer exists yet.
-    if (RefPtr<PresShell> presShell = docShell->GetPresShell()) {
-      presShell->ActivenessMaybeChanged();
-    }
+  PresShellActivenessMaybeChanged();
+}
+
+IPCResult BrowserChild::RecvPreserveLayers(bool aPreserve) {
+  mIsPreservingLayers = true;
+
+  PresShellActivenessMaybeChanged();
+
+  return IPC_OK();
+}
+
+void BrowserChild::PresShellActivenessMaybeChanged() {
+  // We don't use BrowserChildBase::GetPresShell() here because that would
+  // create a content viewer if one doesn't exist yet. Creating a content
+  // viewer can cause JS to run, which we want to avoid.
+  // nsIDocShell::GetPresShell returns null if no content viewer exists yet.
+  //
+  // When this method is called we don't want to go through the browsing context
+  // because we don't want to change the visibility state of the document, which
+  // has side effects like firing events to content, unblocking media playback,
+  // unthrottling timeouts... PresShell activeness has a lot less side effects.
+  nsCOMPtr<nsIDocShell> docShell = do_GetInterface(WebNavigation());
+  if (!docShell) {
+    return;
   }
+  RefPtr<PresShell> presShell = docShell->GetPresShell();
+  if (!presShell) {
+    return;
+  }
+  presShell->ActivenessMaybeChanged();
 }
 
 NS_IMETHODIMP

dom/ipc/BrowserChild.h

@@ -486,6 +486,7 @@ class BrowserChild final : public nsMessageManagerScriptExecutor,
                            nsTArray<CommandInt>& aCommands);
 
   bool IsVisible();
+  bool IsPreservingLayers() const { return mIsPreservingLayers; }
 
   /**
    * Signal to this BrowserChild that it should be made visible:
@@ -495,6 +496,7 @@ class BrowserChild final : public nsMessageManagerScriptExecutor,
   MOZ_CAN_RUN_SCRIPT void UpdateVisibility();
   MOZ_CAN_RUN_SCRIPT void MakeVisible();
   void MakeHidden();
+  void PresShellActivenessMaybeChanged();
 
   ContentChild* Manager() const { return mManager; }
 
@@ -713,6 +715,8 @@ class BrowserChild final : public nsMessageManagerScriptExecutor,
   mozilla::ipc::IPCResult RecvRenderLayers(
       const bool& aEnabled, const layers::LayersObserverEpoch& aEpoch);
 
+  mozilla::ipc::IPCResult RecvPreserveLayers(bool);
+
   mozilla::ipc::IPCResult RecvNavigateByKey(const bool& aForward,
                                             const bool& aForDocumentNavigation);
 
@@ -889,6 +893,9 @@ class BrowserChild final : public nsMessageManagerScriptExecutor,
   // Whether we are rendering to the compositor or not.
   bool mRenderLayers;
 
+  // Whether we're artificially preserving layers.
+  bool mIsPreservingLayers;
+
   // In some circumstances, a DocShell might be in a state where it is
   // "blocked", and we should not attempt to change its active state or
   // the underlying PresShell state until the DocShell becomes unblocked.

dom/ipc/BrowserParent.cpp

@@ -222,7 +222,7 @@ BrowserParent::BrowserParent(ContentParent* aManager, const TabId& aTabId,
       mMarkedDestroying(false),
       mIsDestroyed(false),
       mRemoteTargetSetsCursor(false),
-      mPreserveLayers(false),
+      mIsPreservingLayers(false),
       mRenderLayers(true),
       mHasLayers(false),
       mHasPresented(false),
@@ -3377,7 +3377,7 @@ bool BrowserParent::GetRenderLayers() { return mRenderLayers; }
 
 void BrowserParent::SetRenderLayers(bool aEnabled) {
   if (aEnabled == mRenderLayers) {
-    if (aEnabled && mHasLayers && mPreserveLayers) {
+    if (aEnabled && mHasLayers && mIsPreservingLayers) {
       // RenderLayers might be called when we've been preserving layers,
       // and already had layers uploaded. In that case, the MozLayerTreeReady
       // event will not naturally arrive, which can confuse the front-end
@@ -3396,7 +3396,7 @@ void BrowserParent::SetRenderLayers(bool aEnabled) {
 
   // Preserve layers means that attempts to stop rendering layers
   // will be ignored.
-  if (!aEnabled && mPreserveLayers) {
+  if (!aEnabled && mIsPreservingLayers) {
     return;
   }
 
@@ -3420,7 +3420,11 @@ void BrowserParent::SetRenderLayersInternal(bool aEnabled) {
 }
 
 void BrowserParent::PreserveLayers(bool aPreserveLayers) {
-  mPreserveLayers = aPreserveLayers;
+  if (mIsPreservingLayers == aPreserveLayers) {
+    return;
+  }
+  mIsPreservingLayers = aPreserveLayers;
+  Unused << SendPreserveLayers(aPreserveLayers);
 }
 
 void BrowserParent::NotifyResolutionChanged() {

dom/ipc/BrowserParent.h

@@ -950,7 +950,7 @@ class BrowserParent final : public PBrowserParent,
 
   // If this flag is set, then the tab's layers will be preserved even when
   // the tab's docshell is inactive.
-  bool mPreserveLayers : 1;
+  bool mIsPreservingLayers : 1;
 
   // Holds the most recent value passed to the RenderLayers function. This
   // does not necessarily mean that the layers have finished rendering

dom/ipc/PBrowser.ipdl

@@ -889,6 +889,12 @@ child:
      *        PaintWhileInterruptingJS).
      */
     async RenderLayers(bool aEnabled, LayersObserverEpoch aEpoch);
+
+    /**
+     * Communicates the child that we want layers to be preserved even when the
+     * browser is inactive.
+     */
+    async PreserveLayers(bool aPreserve);
 child:
     /**
      * Notify the child that it shouldn't paint the offscreen displayport.

layout/base/PresShell.cpp

@@ -10797,7 +10797,16 @@ bool PresShell::ShouldBeActive() const {
     // throttling code (in-process throttling for non-visible iframes lives
     // right now in Document::ShouldThrottleFrameRequests(), but that only
     // throttles rAF).
-    return browserChild->IsVisible();
+    if (!browserChild->IsVisible()) {
+      return false;
+    }
+
+    // If the browser is visible but just due to be preserving layers
+    // artificially, we do want to fall back to the browsing context activeness
+    // instead. Otherwise we do want to be active for the use cases above.
+    if (!browserChild->IsPreservingLayers()) {
+      return true;
+    }
   }
 
   BrowsingContext* bc = doc->GetBrowsingContext();