compositor-worker: Initialize CW machinery plumbing to compositor and fire CW rAF callbacks.

third_party/WebKit/Source/web/WebViewImpl.h

 /*
  * Copyright (C) 2010 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 69 matching lines @@
 class PaintLayerCompositor;
 class TopControls;
 class UserGestureToken;
 class WebActiveGestureAnimation;
 class WebDevToolsAgentImpl;
 class WebElement;
 class WebLayerTreeView;
 class WebLocalFrame;
 class WebLocalFrameImpl;
 class WebImage;
+class CompositorMutatorImpl;
 class WebPagePopupImpl;
 class WebPlugin;
 class WebRemoteFrame;
 class WebSelection;
 class WebSettingsImpl;
 class WebViewScheduler;
 
 class WEB_EXPORT WebViewImpl final : WTF_NON_EXPORTED_BASE(public WebView)
     , public RefCounted<WebViewImpl>
     , WTF_NON_EXPORTED_BASE(public WebGestureCurveTarget)
@@ skipping 395 matching lines @@
 
     void updateTopControlsState(WebTopControlsState constraint, WebTopControlsState current, bool animate) override;
 
     TopControls& topControls();
     // Called anytime top controls layout height or content offset have changed.
     void didUpdateTopControls();
 
     void forceNextWebGLContextCreationToFail() override;
     void forceNextDrawingBufferCreationToFail() override;
 
+    CompositorProxyClient* createCompositorProxyClient();
     IntSize mainFrameSize();
     WebDisplayMode displayMode() const { return m_displayMode; }
 
     PageScaleConstraintsSet& pageScaleConstraintsSet() const;
 
     FloatSize elasticOverscroll() const { return m_elasticOverscroll; }
 
     // Attaches the PaintArtifactCompositor's tree to this WebView's layer tree
     // view.
     void attachPaintArtifactCompositor();
@@ skipping 221 matching lines @@
     float m_zoomFactorOverride;
 
     bool m_userGestureObserved;
     bool m_shouldDispatchFirstVisuallyNonEmptyLayout;
     bool m_shouldDispatchFirstLayoutAfterFinishedParsing;
     bool m_shouldDispatchFirstLayoutAfterFinishedLoading;
     WebDisplayMode m_displayMode;
 
     FloatSize m_elasticOverscroll;
 
+    // This is owned by the LayerTreeHostImpl, and should only be used on the
+    // compositor thread. The LayerTreeHostImpl is indirectly owned by this
+    // class so this pointer should be valid until this class is destructed.

[haraken, 2016/05/06 02:45:51]

Then can we remove the m_mutator by looking up the mutator via
LayerTreeHostImpl? It's not a good idea to introduce an unnecessary
CrossThreadPersistent because it might cause leaks.

[flackr, 2016/05/06 18:15:08]

We might technically be able to get it through WebLayerTreeView -> LayerTreeHost
-> Proxy-> ChannelMain -> LayerTreeHostImpl -> CompositorThreadOnly -> ProxyImpl
-> LayerTreeHostImpl, but not only is that a long path which needs to include
the thread hop, I'm somewhat concerned about race conditions on creating the
CompositorMutatorImpl. LayerTreeHostImpl can't create it because it's in cc/, so
because we create it in WebViewImpl and it eventually makes it over there, we
won't know if we get a nullptr response whether there is already a
CompositorMutatorImpl in flight waiting for the next commit to be sent over to
LayerTreeHostImpl.

Jeremy and I had an idea for how WebViewImpl could make a a callback, and pass
it to the LayerTreeHostImpl to run to create the CompositorMutatorImpl, however
Dana had concerns with the extra interfaces necessary for this kind of a
callback.

If I understand your concern, having m_mutator could keep the
CompositorMutatorImpl alive? It looks like resetting the pointer in
WebViewImpl::willCloseLayerTreeView might protect against this.

+    CrossThreadPersistent<CompositorMutatorImpl> m_mutator;
+
     Persistent<EventListener> m_popupMouseWheelEventListener;
 
     WebPageImportanceSignals m_pageImportanceSignals;
 
     const OwnPtr<WebViewScheduler> m_scheduler;
 
     // Manages the layer tree created for this page in Slimming Paint v2.
     PaintArtifactCompositor m_paintArtifactCompositor;
 
     double m_lastFrameTimeMonotonic;
 };
 
 DEFINE_TYPE_CASTS(WebViewImpl, WebWidget, widget, widget->isWebView(), widget.isWebView());
 // We have no ways to check if the specified WebView is an instance of
 // WebViewImpl because WebViewImpl is the only implementation of WebView.
 DEFINE_TYPE_CASTS(WebViewImpl, WebView, webView, true, true);
 
 } // namespace blink
 
 #endif