Implement top controls show/hide functionality for main thread scrolling

public/platform/WebLayerTreeView.h

Index: public/platform/WebLayerTreeView.h
diff --git a/public/platform/WebLayerTreeView.h b/public/platform/WebLayerTreeView.h
index d268c96e157089748982ff9a6d5868c00069a1cb..86889fac59e447c4d72fd2c6f132ce719adbde28 100644
--- a/public/platform/WebLayerTreeView.h
+++ b/public/platform/WebLayerTreeView.h
@@ -32,6 +32,7 @@
 #include "WebNonCopyable.h"
 #include "WebPrivateOwnPtr.h"
 #include "WebSize.h"
+#include "public/web/WebTopControlsState.h"
 
 class SkBitmap;
 
@@ -41,6 +42,7 @@ class WebCompositeAndReadbackAsyncCallback;
 class WebLayer;
 struct WebPoint;
 struct WebSelectionBound;
+class WebWidget;
 
 class WebLayerTreeView {
 public:
@@ -86,6 +88,16 @@ public:
     // (fully shown).
     virtual void setTopControlsShownRatio(float) { }
 
+    // Update top controls permitted and current states
+    virtual void updateTopControlsState(WebTopControlsState constraints, WebTopControlsState current, bool animate) { }
+
+    // If this is set to true, then the embedder shrunk the WebView size by the top

[aelias_OOO_until_Jul13, 2015/02/13 02:03:17]

Please update the comment to say that this means Blink shrunk the viewport clip
layers by the top control height, as that's the relevant meaning from the point
of view of CC.

[majidvp, 2015/02/18 21:03:57]

Done.

+    // controls height.
+    virtual void setTopControlsShrinkBlinkSize(bool shrink) { }
+
+    // Set top controls height
+    virtual void setTopControlsHeight(float height) { }
+
     // Flow control and scheduling ---------------------------------------
 
     // Indicates that an animation needs to be updated.