Throttle rendering pipeline for invisible iframes

Source/core/frame/FrameView.h

Index: Source/core/frame/FrameView.h
diff --git a/Source/core/frame/FrameView.h b/Source/core/frame/FrameView.h
index a1b2b4383ff62b44434aa193bdc964110947d04a..65a58bbdb3d3a33573d8f3d4aba881c8cee8d7f2 100644
--- a/Source/core/frame/FrameView.h
+++ b/Source/core/frame/FrameView.h
@@ -226,11 +226,14 @@ public:
     Color documentBackgroundColor() const;
 
     // Run all needed lifecycle stages. After calling this method, all frames will be in the lifecycle state PaintInvalidationClean.
-    void updateAllLifecyclePhases();
+    // If lifecycle throttling is allowed, some frames may skip the lifecycle update (e.g., based on visibility) and will not end
+    // up being PaintInvalidationClean.
+    enum class LifecycleThrottlingMode { Disallow, Allow };
+    void updateAllLifecyclePhases(LifecycleThrottlingMode = LifecycleThrottlingMode::Disallow);
 
     // Computes the style, layout and compositing lifecycle stages if needed. After calling this method, all frames wil lbe in a lifecycle
     // state >= CompositingClean, and scrolling has been updated.
-    void updateLifecycleToCompositingCleanPlusScrolling();
+    void updateLifecycleToCompositingCleanPlusScrolling(LifecycleThrottlingMode = LifecycleThrottlingMode::Disallow);
 
     bool invalidateViewportConstrainedObjects();
 
@@ -559,6 +562,19 @@ public:
     void setFrameTimingRequestsDirty(bool isDirty) { m_frameTimingRequestsDirty = isDirty; }
     bool frameTimingRequestsDirty() { return m_frameTimingRequestsDirty; }
 
+    // Returns true if this frame should skip rendering pipeline processing during the
+    // current BeginMainFrame.
+    bool shouldThrottleRenderingPipeline() const;
+
+    // Returns true if this frame should skip style computation, layout and
+    // compositing updates for the current BeginMainFrame.
+    bool shouldThrottleStyleLayoutAndCompositingUpdates() const;
+
+    // Updates the throttling status of all frames in the hierarchy and
+    // schedules new animations or lifecycle updates as necessary. Must be
+    // called after the layer update phase of the current BeginMainFrame.
+    void updateThrottling();
+
 protected:
     // Scroll the content via the compositor.
     bool scrollContentsFastPath(const IntSize& scrollDelta);
@@ -612,7 +628,7 @@ private:
         OnlyUpToCompositingCleanPlusScrolling,
     };
 
-    void updateLifecyclePhasesInternal(LifeCycleUpdateOption);
+    void updateLifecyclePhasesInternal(LifeCycleUpdateOption, LifecycleThrottlingMode);
     void invalidateTreeIfNeededRecursive();
     void scrollContentsIfNeededRecursive();
     void updateStyleAndLayoutIfNeededRecursive();
@@ -717,6 +733,10 @@ private:
     void collectFrameTimingRequests(GraphicsLayerFrameTimingRequests&);
     void collectFrameTimingRequestsRecursive(GraphicsLayerFrameTimingRequests&);
 
+    void computeViewportVisibility();
+    void setLifecycleThrottlingModeRecursive(LifecycleThrottlingMode);
+    void updateThrottlingRecursive(bool hasCrossedSecurityOrigin);
+
     LayoutSize m_size;
 
     typedef HashSet<RefPtr<LayoutEmbeddedObject>> EmbeddedObjectSet;
@@ -839,6 +859,15 @@ private:
     // TODO(bokan): crbug.com/484188. We should specialize FrameView for the
     // main frame.
     OwnPtrWillBeMember<ScrollableArea> m_viewportScrollableArea;
+
+    LifecycleThrottlingMode m_lifecycleThrottlingMode;
+    // This frame's bounds in the root frame's content coordinates, clipped recursively through every ancestor view.
+    IntRect m_clippedBounds;
+
+    enum class ViewportVisibility { Hidden, Visible, Unknown };
+    ViewportVisibility m_viewportVisibility;
+    ViewportVisibility m_viewportVisibilityForThrottling;

[ojan, 2015/09/01 19:56:48]

This member deserves a comment explaining why we need to the variables, i.e.
that we need to compute the visibility when the frame moves but not update it
until after the current frame of the pipeline is finished to avoid violating
assumptions of the layout/painting code.

[Sami, 2015/09/02 10:46:02]

Definitely agreed. Added a comment.

+    bool m_isCrossOriginForThrottling;
 };
 
 inline void FrameView::incrementVisuallyNonEmptyCharacterCount(unsigned count)