Made top controls work with virtual viewport pinch-to-zoom. (Blink)

Source/core/frame/PinchViewport.h

Index: Source/core/frame/PinchViewport.h
diff --git a/Source/core/frame/PinchViewport.h b/Source/core/frame/PinchViewport.h
index 6ab9b65a16a32d419cfd42fddd04225dd148e964..7eb31e9734e616c223b2aa69e97526902baae76a 100644
--- a/Source/core/frame/PinchViewport.h
+++ b/Source/core/frame/PinchViewport.h
@@ -87,7 +87,6 @@ public:
     FloatPoint location() const { return m_offset; }
 
     // Sets the size of the inner viewport when unscaled in CSS pixels.
-    // This will be clamped to the size of the outer viewport (the main frame).
     void setSize(const IntSize&);
     IntSize size() const { return m_size; }
 
@@ -122,6 +121,14 @@ public:
     // scroll extents of the viewport within the document.
     IntPoint clampDocumentOffsetAtScale(const IntPoint& offset, float scale);
 
+    // FIXME: This is kind of a hack. Ideally, we would just resize the
+    // viewports to account for top controls. However, FrameView includes much
+    // more than just scrolling so we can't simply resize it without incurring
+    // all sorts of side-effects. Until we can seperate out the scrollability
+    // aspect from FrameView, we use this method to let PinchViewport make the
+    // necessary adjustments so that we don't incorrectly clamp scroll offsets
+    // coming from the compositor. crbug.com/422328
+    void setTopControlsAdjustment(float);
 private:
     explicit PinchViewport(FrameHost&);
 
@@ -179,6 +186,7 @@ private:
     FloatPoint m_offset;
     float m_scale;
     IntSize m_size;
+    float m_topControlsAdjustment;
 };
 
 } // namespace blink