Make all methods on WebLayerTreeView optional.

public/platform/WebLayerTreeView.h

 /*
  * Copyright (C) 2011 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:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 36 matching lines @@
 class WebSelection;
 class WebWidget;
 
 class WebLayerTreeView {
 public:
     virtual ~WebLayerTreeView() { }
 
     // Initialization and lifecycle --------------------------------------
 
     // Sets the root of the tree. The root is set by way of the constructor.
-    virtual void setRootLayer(const WebLayer&) = 0;
-    virtual void clearRootLayer() = 0;
+    virtual void setRootLayer(const WebLayer&) { }
+    virtual void clearRootLayer() { }
 
     virtual void attachCompositorAnimationTimeline(WebCompositorAnimationTimeline*) { }
     virtual void detachCompositorAnimationTimeline(WebCompositorAnimationTimeline*) { }
 
     // View properties ---------------------------------------------------
 
-    virtual void setViewportSize(const WebSize& deviceViewportSize) = 0;
+    virtual void setViewportSize(const WebSize& deviceViewportSize) { }
     // Gives the viewport size in physical device pixels.
-    virtual WebSize deviceViewportSize() const = 0;
+    virtual WebSize deviceViewportSize() const { return WebSize(); }
 
-    virtual void setDeviceScaleFactor(float) = 0;
-    virtual float deviceScaleFactor() const = 0;
+    virtual void setDeviceScaleFactor(float) { }
+    virtual float deviceScaleFactor() const { return 0; }
 
     // Sets the background color for the viewport.
-    virtual void setBackgroundColor(WebColor) = 0;
+    virtual void setBackgroundColor(WebColor) { }
 
     // Sets the background transparency for the viewport. The default is 'false'.
-    virtual void setHasTransparentBackground(bool) = 0;
+    virtual void setHasTransparentBackground(bool) { }
 
     // Sets whether this view is visible. In threaded mode, a view that is not visible will not
     // composite or trigger updateAnimations() or layout() calls until it becomes visible.
-    virtual void setVisible(bool) = 0;
+    virtual void setVisible(bool) { }
 
     // Sets the current page scale factor and minimum / maximum limits. Both limits are initially 1 (no page scale allowed).
-    virtual void setPageScaleFactorAndLimits(float pageScaleFactor, float minimum, float maximum) = 0;
+    virtual void setPageScaleFactorAndLimits(float pageScaleFactor, float minimum, float maximum) { }
 
     // Starts an animation of the page scale to a target scale factor and scroll offset.
     // If useAnchor is true, destination is a point on the screen that will remain fixed for the duration of the animation.
     // If useAnchor is false, destination is the final top-left scroll position.
-    virtual void startPageScaleAnimation(const WebPoint& destination, bool useAnchor, float newPageScale, double durationSec) = 0;
+    virtual void startPageScaleAnimation(const WebPoint& destination, bool useAnchor, float newPageScale, double durationSec) { }
 
     virtual void heuristicsForGpuRasterizationUpdated(bool) { }
 
     // Sets the amount that the top controls are showing, from 0 (hidden) to 1
     // (fully shown).
     virtual void setTopControlsShownRatio(float) { }
 
     // Update top controls permitted and current states
     virtual void updateTopControlsState(WebTopControlsState constraints, WebTopControlsState current, bool animate) { }
 
@@ skipping 24 matching lines @@
     // The caller is resposible for keeping the WebLayoutAndPaintAsyncCallback object
     // alive until it is called.
     virtual void layoutAndPaintAsync(WebLayoutAndPaintAsyncCallback*) { }
 
     // The caller is responsible for keeping the WebCompositeAndReadbackAsyncCallback
     // object alive until it is called.
     virtual void compositeAndReadbackAsync(WebCompositeAndReadbackAsyncCallback*) { }
 
     // Blocks until the most recently composited frame has finished rendering on the GPU.
     // This can have a significant performance impact and should be used with care.
-    virtual void finishAllRendering() = 0;
+    virtual void finishAllRendering() { }
 
     // Prevents updates to layer tree from becoming visible.
     virtual void setDeferCommits(bool deferCommits) { }
 
     // Take responsiblity for this layer's animations, even if this layer hasn't yet
     // been added to the tree.
     virtual void registerForAnimations(WebLayer* layer) { }
 
     // Identify key layers to the compositor when using the pinch virtual viewport.
     virtual void registerViewportLayers(
@@ skipping 25 matching lines @@
     // Toggles continuous painting
     virtual void setContinuousPaintingEnabled(bool) { }
 
     // Toggles scroll bottleneck rects on the HUD layer
     virtual void setShowScrollBottleneckRects(bool) { }
 };
 
 } // namespace blink
 
 #endif // WebLayerTreeView_h