Implement desktop compatibility viewport

cc/layer_impl.h

Index: cc/layer_impl.h
diff --git a/cc/layer_impl.h b/cc/layer_impl.h
index c05fb5539017b73a4b69a4cc12b6e115325f61da..032d5cc5333a2e0b6e769d1d8ea63320bda85909 100644
--- a/cc/layer_impl.h
+++ b/cc/layer_impl.h
@@ -229,6 +229,15 @@ public:
     const gfx::Vector2d& sentScrollDelta() const { return m_sentScrollDelta; }
     void setSentScrollDelta(const gfx::Vector2d& sentScrollDelta);
 
+    const gfx::Vector2d& desktopCompatibilityViewportOffsetFromScrollPosition() { return m_desktopCompatibilityViewportOffsetFromScrollPosition; }
+    void setDesktopCompatibilityViewportOffsetFromScrollPosition(const gfx::Vector2d& desktopCompatibilityViewportOffsetFromScrollPosition) { m_desktopCompatibilityViewportOffsetFromScrollPosition = desktopCompatibilityViewportOffsetFromScrollPosition; }
+
+    const gfx::Vector2dF& desktopCompatibilityViewportOffsetFromScrollPositionDelta() { return m_desktopCompatibilityViewportOffsetFromScrollPositionDelta; }
+    void setDesktopCompatibilityViewportOffsetFromScrollPositionDelta(const gfx::Vector2dF& desktopCompatibilityViewportOffsetFromScrollPositionDelta) { m_desktopCompatibilityViewportOffsetFromScrollPositionDelta = desktopCompatibilityViewportOffsetFromScrollPositionDelta; }
+
+    const gfx::Vector2d& sentDesktopCompatibilityViewportOffsetFromScrollPositionDelta() { return m_sentDesktopCompatibilityViewportOffsetFromScrollPositionDelta; }
+    void setSentDesktopCompatibilityViewportOffsetFromScrollPositionDelta(const gfx::Vector2d& sentDesktopCompatibilityViewportOffsetFromScrollPositionDelta) { m_sentDesktopCompatibilityViewportOffsetFromScrollPositionDelta = sentDesktopCompatibilityViewportOffsetFromScrollPositionDelta; }
+
     // Returns the delta of the scroll that was outside of the bounds of the initial scroll
     gfx::Vector2dF scrollBy(const gfx::Vector2dF& scroll);
 
@@ -391,6 +400,10 @@ private:
     gfx::Vector2d m_maxScrollOffset;
     gfx::Transform m_implTransform;
     gfx::Vector2dF m_lastScrollOffset;
+    // For root scroll layer only.
+    gfx::Vector2d m_desktopCompatibilityViewportOffsetFromScrollPosition;
+    gfx::Vector2dF m_desktopCompatibilityViewportOffsetFromScrollPositionDelta;
+    gfx::Vector2d m_sentDesktopCompatibilityViewportOffsetFromScrollPositionDelta;
 
     // The global depth value of the center of the layer. This value is used
     // to sort layers from back to front.