Bug 1290420 Part 4: Make the PresShell create a MobileViewportManager on demand. r=botond,smaug

Depends on D3376

Differential Revision: https://phabricator.services.mozilla.com/D3377

--HG--
extra : moz-landing-system : lando

docshell/base/nsDocShell.cpp

@@ -2662,6 +2662,13 @@ nsDocShell::SetMetaViewportOverride(uint32_t aMetaViewportOverride)
 
   mMetaViewportOverride = aMetaViewportOverride;
 
+  // Inform our presShell that it needs to re-check its need for a viewport
+  // override.
+  nsCOMPtr<nsIPresShell> presShell = GetPresShell();
+  if (presShell) {
+    presShell->UpdateViewportOverridden(true);
+  }
+
   return NS_OK;
 }
 

layout/base/MobileViewportManager.h

@@ -56,13 +56,14 @@ public:
    * updated, and the SPCSPS needs to be updated. */
   void ResolutionUpdated();
 
-private:
-  ~MobileViewportManager();
-
   /* Called to compute the initial viewport on page load or before-first-paint,
-   * whichever happens first. */
+   * whichever happens first. Also called directly if we are created after the
+   * presShell is initialized. */
   void SetInitialViewport();
 
+  private:
+  ~MobileViewportManager();
+
   /* Main helper method to update the CSS viewport and any other properties that
    * need updating. */
   void RefreshViewportSize(bool aForceAdjustResolution);

layout/base/PresShell.cpp

@@ -1045,9 +1045,9 @@ PresShell::Init(nsIDocument* aDocument,
   if (mPresContext->IsRootContentDocument()) {
     mZoomConstraintsClient = new ZoomConstraintsClient();
     mZoomConstraintsClient->Init(this, mDocument);
-    if (nsLayoutUtils::ShouldHandleMetaViewport(mDocument) || gfxPrefs::APZAllowZooming()) {
-      mMobileViewportManager = new MobileViewportManager(this, mDocument);
-    }
+
+    // We call this to create mMobileViewportManager, if it is needed.
+    UpdateViewportOverridden(false);
   }
 }
 
@@ -10496,6 +10496,49 @@ PresShell::SetIsActive(bool aIsActive)
   return rv;
 }
 
+void
+PresShell::UpdateViewportOverridden(bool aAfterInitialization)
+{
+  // Determine if we require a MobileViewportManager.
+  bool needMVM = nsLayoutUtils::ShouldHandleMetaViewport(mDocument) ||
+                 gfxPrefs::APZAllowZooming();
+
+  if (needMVM == !!mMobileViewportManager) {
+    // Either we've need one and we've already got it, or we don't need one
+    // and don't have it. Either way, we're done.
+    return;
+  }
+
+  if (needMVM) {
+    if (mPresContext->IsRootContentDocument()) {
+      mMobileViewportManager = new MobileViewportManager(this, mDocument);
+
+      if (aAfterInitialization) {
+        // Setting the initial viewport will trigger a reflow.
+        mMobileViewportManager->SetInitialViewport();
+      }
+    }
+    return;
+  }
+
+  MOZ_ASSERT(mMobileViewportManager, "Shouldn't reach this without a "
+                                     "MobileViewportManager.");
+  mMobileViewportManager->Destroy();
+  mMobileViewportManager = nullptr;
+
+  if (aAfterInitialization) {
+    // Force a reflow to our correct size by going back to the docShell
+    // and asking it to reassert its size. This is necessary because
+    // everything underneath the docShell, like the ViewManager, has been
+    // altered by the MobileViewportManager in an irreversible way.
+    nsDocShell* docShell =
+      static_cast<nsDocShell*>(GetPresContext()->GetDocShell());
+    int32_t width, height;
+    docShell->GetSize(&width, &height);
+    docShell->SetSize(width, height, false);
+  }
+}
+
 /*
  * Determines the current image locking state. Called when one of the
  * dependent factors changes.

layout/base/PresShell.h

@@ -345,6 +345,8 @@ public:
     return (mMobileViewportManager != nullptr);
   }
 
+  void UpdateViewportOverridden(bool aAfterInitialization) override;
+
   bool IsLayoutFlushObserver() override
   {
     return GetPresContext()->RefreshDriver()->

layout/base/nsIPresShell.h

@@ -366,10 +366,16 @@ public:
                        ResizeReflowOptions::eBSizeExact) = 0;
 
   /**
-   * Returns true if ResizeReflowOverride has been called.
+   * Returns true if the platform/pref or docshell require a meta viewport.
    */
   virtual bool GetIsViewportOverridden() = 0;
 
+  /**
+   * Note that the assumptions that determine the need for a meta viewport
+   * may have changed.
+   */
+  virtual void UpdateViewportOverridden(bool aAfterInitialization) = 0;
+
   /**
    * Return true if the presshell expects layout flush.
    */