Introduce bottom controls to CC and let it respond to scrolling

cc/input/top_controls_manager.h

Index: cc/input/top_controls_manager.h
diff --git a/cc/input/top_controls_manager.h b/cc/input/top_controls_manager.h
index 4ec45776e99e9f7452a65fc2762dec48f5d68213..91a52737271b8d09dceca385b797062f22007505 100644
--- a/cc/input/top_controls_manager.h
+++ b/cc/input/top_controls_manager.h
@@ -36,11 +36,21 @@ class CC_EXPORT TopControlsManager
       float top_controls_hide_threshold);
   virtual ~TopControlsManager();
 
+  // The amount of offset to translate the top controls. 0 or negative value.

[bokan, 2016/07/01 17:19:13]

Thanks for adding comments.

Suggested change here, how about "The offset from the window top to the top edge
of the controls. Runs from 0 (controls fully shown) to negative values (down is
positive)." It's a bit ambiguous unless you know which edges you're measuring
and where 0 is.

[Ian Wen, 2016/07/06 20:53:44]

done.

   float ControlsTopOffset() const;
+  // The amount of offset of the web content area. Same as the current shown
+  // height of the top controls.
   float ContentTopOffset() const;
   float TopControlsShownRatio() const;
   float TopControlsHeight() const;

[bokan, 2016/07/01 17:19:14]

Please comment that this is a static value. The actual offset is calculated
using the shown ratio.

[Ian Wen, 2016/07/06 20:53:44]

Done.

 
+  // The amount of offset to translate the bottom controls. 0 or positive value.
+  float ControlsBottomOffset() const;
+  // The amount of offset of the web content area, calculating from the bottom.
+  // Same as the current shown height of the bottom controls.
+  float ContentBottomOffset() const;
+  float BottomControlsHeight() const;
+
   bool has_animation() const { return animation_direction_ != NO_ANIMATION; }
   AnimationDirection animation_direction() { return animation_direction_; }