Bug 1668875 - Invalidate images for media query changes more granularly. r=heycam

The SVG code invalidating too much causes hangs with pages that have
lots of SVGs.

Differential Revision: https://phabricator.services.mozilla.com/D94186

image/VectorImage.cpp

@@ -1556,20 +1556,16 @@ void VectorImage::MediaFeatureValuesChangedAllDocuments(
   }
 
   if (Document* doc = mSVGDocumentWrapper->GetDocument()) {
-    if (nsPresContext* presContext = doc->GetPresContext()) {
+    if (RefPtr<nsPresContext> presContext = doc->GetPresContext()) {
       presContext->MediaFeatureValuesChangedAllDocuments(aChange);
       // Media feature value changes don't happen in the middle of layout,
       // so we don't need to call InvalidateObserversOnNextRefreshDriverTick
       // to invalidate asynchronously.
-      //
-      // Ideally we would not invalidate images if the media feature value
-      // change did not cause any updates to the document, but since non-
-      // animated SVG images do not have their refresh driver ticked, it
-      // is the invalidation (and then the painting) which is what causes
-      // the document to be flushed. Theme and system metrics changes are
-      // rare, though, so it's not a big deal to invalidate even if it
-      // doesn't cause any change.
-      SendInvalidationNotifications();
+      if (presContext->FlushPendingMediaFeatureValuesChanged()) {
+        // NOTE(emilio): SendInvalidationNotifications flushes layout via
+        // VectorImage::CreateSurface -> FlushImageTransformInvalidation.
+        SendInvalidationNotifications();
+      }
     }
   }
 }

layout/base/nsPresContext.cpp

@@ -1562,9 +1562,9 @@ void nsPresContext::MediaFeatureValuesChangedAllDocuments(
   }
 }
 
-void nsPresContext::FlushPendingMediaFeatureValuesChanged() {
+bool nsPresContext::FlushPendingMediaFeatureValuesChanged() {
   if (!mPendingMediaFeatureValuesChange) {
-    return;
+    return false;
   }
 
   MediaFeatureChange change = *mPendingMediaFeatureValuesChange;
@@ -1576,13 +1576,14 @@ void nsPresContext::FlushPendingMediaFeatureValuesChanged() {
         mPresShell->StyleSet()->MediumFeaturesChanged(change.mReason);
   }
 
-  if (change.mRestyleHint || change.mChangeHint) {
+  const bool changedStyle = change.mRestyleHint || change.mChangeHint;
+  if (changedStyle) {
     RebuildAllStyleData(change.mChangeHint, change.mRestyleHint);
   }
 
   if (mDocument->IsBeingUsedAsImage()) {
     MOZ_ASSERT(mDocument->MediaQueryLists().isEmpty());
-    return;
+    return changedStyle;
   }
 
   mDocument->NotifyMediaFeatureValuesChanged();
@@ -1600,7 +1601,7 @@ void nsPresContext::FlushPendingMediaFeatureValuesChanged() {
   // style sheets has been computed.
 
   if (mDocument->MediaQueryLists().isEmpty()) {
-    return;
+    return changedStyle;
   }
 
   // We build a list of all the notifications we're going to send
@@ -1613,14 +1614,18 @@ void nsPresContext::FlushPendingMediaFeatureValuesChanged() {
     }
   }
 
-  nsContentUtils::AddScriptRunner(NS_NewRunnableFunction(
-      "nsPresContext::FlushPendingMediaFeatureValuesChanged",
-      [list = std::move(listsToNotify)] {
-        for (const auto& mql : list) {
-          nsAutoMicroTask mt;
-          mql->FireChangeEvent();
-        }
-      }));
+  if (!listsToNotify.IsEmpty()) {
+    nsContentUtils::AddScriptRunner(NS_NewRunnableFunction(
+        "nsPresContext::FlushPendingMediaFeatureValuesChanged",
+        [list = std::move(listsToNotify)] {
+          for (const auto& mql : list) {
+            nsAutoMicroTask mt;
+            mql->FireChangeEvent();
+          }
+        }));
+  }
+
+  return changedStyle;
 }
 
 void nsPresContext::SizeModeChanged(nsSizeMode aSizeMode) {

layout/base/nsPresContext.h

@@ -290,7 +290,8 @@ class nsPresContext : public nsISupports, public mozilla::SupportsWeakPtr {
    */
   void MediaFeatureValuesChanged(const mozilla::MediaFeatureChange& aChange);
 
-  void FlushPendingMediaFeatureValuesChanged();
+  /** Returns whether any media query changed. */
+  bool FlushPendingMediaFeatureValuesChanged();
 
   /**
    * Calls MediaFeatureValuesChanged for this pres context and all descendant