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..bcc5f1e858d19d0aecc2c98df715b938dc137bec 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 "WebTopControlsState.h"
 
 class SkBitmap;
 
@@ -41,6 +42,7 @@ class WebCompositeAndReadbackAsyncCallback;
 class WebLayer;
 struct WebPoint;
 struct WebSelectionBound;
+class WebWidget;
 
 class WebLayerTreeView {
 public:
@@ -86,6 +88,13 @@ public:
     // (fully shown).
     virtual void setTopControlsShownRatio(float) { }
 
+    // Update top controls permitted and current states
+    virtual void updateTopControlsState(WebTopControlsState constraints, WebTopControlsState current, bool animate) { }
+
+    // Set top controls height. If |shrinkViewport| is set to true, then Blink shrunk the viewport clip
+    // layers by the top controls height.
+    virtual void setTopControlsHeight(float height, bool shrinkViewport) { }
+
     // Flow control and scheduling ---------------------------------------
 
     // Indicates that an animation needs to be updated.