Bug 1171371 - On memory-pressure, remove any stale images from the visible images list. r=tn

layout/base/nsIPresShell.h

@@ -1570,7 +1570,8 @@ public:
   // Clears the current list of visible images on this presshell and replaces it
   // with images that are in the display list aList.
   virtual void RebuildImageVisibilityDisplayList(const nsDisplayList& aList) = 0;
-  virtual void RebuildImageVisibility(nsRect* aRect = nullptr) = 0;
+  virtual void RebuildImageVisibility(nsRect* aRect = nullptr,
+                                      bool aRemoveOnly = false) = 0;
 
   // Ensures the image is in the list of visible images.
   virtual void EnsureImageInVisibleList(nsIImageLoadingContent* aImage) = 0;

layout/base/nsPresShell.cpp

@@ -920,6 +920,7 @@ PresShell::Init(nsIDocument* aDocument,
 #ifdef MOZ_XUL
       os->AddObserver(this, "chrome-flush-skin-caches", false);
 #endif
+      os->AddObserver(this, "memory-pressure", false);
     }
   }
 
@@ -1144,6 +1145,7 @@ PresShell::Destroy()
 #ifdef MOZ_XUL
       os->RemoveObserver(this, "chrome-flush-skin-caches");
 #endif
+      os->RemoveObserver(this, "memory-pressure");
     }
   }
 
@@ -5587,12 +5589,15 @@ PresShell::ClearVisibleImagesList(uint32_t aNonvisibleAction)
 }
 
 void
-PresShell::MarkImagesInSubtreeVisible(nsIFrame* aFrame, const nsRect& aRect)
+PresShell::MarkImagesInSubtreeVisible(nsIFrame* aFrame,
+                                      const nsRect& aRect,
+                                      bool aRemoveOnly /* = false */)
 {
   MOZ_ASSERT(aFrame->PresContext()->PresShell() == this, "wrong presshell");
 
   nsCOMPtr<nsIImageLoadingContent> content(do_QueryInterface(aFrame->GetContent()));
-  if (content && aFrame->StyleVisibility()->IsVisible()) {
+  if (content && aFrame->StyleVisibility()->IsVisible() &&
+      (!aRemoveOnly || content->GetVisibleCount() > 0)) {
     uint32_t count = mVisibleImages.Count();
     mVisibleImages.PutEntry(content);
     if (mVisibleImages.Count() > count) {
@@ -5673,7 +5678,8 @@ PresShell::MarkImagesInSubtreeVisible(nsIFrame* aFrame, const nsRect& aRect)
 }
 
 void
-PresShell::RebuildImageVisibility(nsRect* aRect)
+PresShell::RebuildImageVisibility(nsRect* aRect,
+                                  bool aRemoveOnly /* = false */)
 {
   MOZ_ASSERT(!mImageVisibilityVisited, "already visited?");
   mImageVisibilityVisited = true;
@@ -5692,7 +5698,7 @@ PresShell::RebuildImageVisibility(nsRect* aRect)
   if (aRect) {
     vis = *aRect;
   }
-  MarkImagesInSubtreeVisible(rootFrame, vis);
+  MarkImagesInSubtreeVisible(rootFrame, vis, aRemoveOnly);
 
   DecrementVisibleCount(oldVisibleImages,
                         nsIImageLoadingContent::ON_NONVISIBLE_NO_ACTION);
@@ -5700,6 +5706,12 @@ PresShell::RebuildImageVisibility(nsRect* aRect)
 
 void
 PresShell::UpdateImageVisibility()
+{
+  DoUpdateImageVisibility(/* aRemoveOnly = */ false);
+}
+
+void
+PresShell::DoUpdateImageVisibility(bool aRemoveOnly)
 {
   MOZ_ASSERT(!mPresContext || mPresContext->IsRootContentDocument(),
     "updating image visibility on a non-root content document?");
@@ -5718,7 +5730,7 @@ PresShell::UpdateImageVisibility()
     return;
   }
 
-  RebuildImageVisibility();
+  RebuildImageVisibility(/* aRect = */ nullptr, aRemoveOnly);
   ClearImageVisibilityVisited(rootFrame->GetView(), true);
 
 #ifdef DEBUG_IMAGE_VISIBILITY_DISPLAY_LIST
@@ -9326,6 +9338,13 @@ PresShell::Observe(nsISupports* aSubject,
     return NS_OK;
   }
 
+  if (!nsCRT::strcmp(aTopic, "memory-pressure") &&
+      !AssumeAllImagesVisible() &&
+      mPresContext->IsRootContentDocument()) {
+    DoUpdateImageVisibility(/* aRemoveOnly = */ true);
+    return NS_OK;
+  }
+
   NS_WARNING("unrecognized topic in PresShell::Observe");
   return NS_ERROR_FAILURE;
 }

layout/base/nsPresShell.h

@@ -374,7 +374,8 @@ public:
   virtual void ScheduleImageVisibilityUpdate() override;
 
   virtual void RebuildImageVisibilityDisplayList(const nsDisplayList& aList) override;
-  virtual void RebuildImageVisibility(nsRect* aRect = nullptr) override;
+  virtual void RebuildImageVisibility(nsRect* aRect = nullptr,
+                                      bool aRemoveOnly = false) override;
 
   virtual void EnsureImageInVisibleList(nsIImageLoadingContent* aImage) override;
 
@@ -726,6 +727,7 @@ protected:
   virtual void ResumePainting() override;
 
   void UpdateImageVisibility();
+  void DoUpdateImageVisibility(bool aRemoveOnly);
   void UpdateActivePointerState(mozilla::WidgetGUIEvent* aEvent);
 
   nsRevocableEventPtr<nsRunnableMethod<PresShell> > mUpdateImageVisibilityEvent;
@@ -733,7 +735,8 @@ protected:
   void ClearVisibleImagesList(uint32_t aNonvisibleAction);
   static void ClearImageVisibilityVisited(nsView* aView, bool aClear);
   static void MarkImagesInListVisible(const nsDisplayList& aList);
-  void MarkImagesInSubtreeVisible(nsIFrame* aFrame, const nsRect& aRect);
+  void MarkImagesInSubtreeVisible(nsIFrame* aFrame, const nsRect& aRect,
+                                  bool aRemoveOnly = false);
 
   // Methods for dispatching KeyboardEvent and BeforeAfterKeyboardEvent.
   void HandleKeyboardEvent(nsINode* aTarget,