Introduce bottom controls to CC and let it respond to scrolling

cc/input/top_controls_manager.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/input/top_controls_manager.h"
 
 #include <stdint.h>
 
 #include <algorithm>
 
@@ skipping 50 matching lines @@
 }
 
 float TopControlsManager::TopControlsShownRatio() const {
   return client_->CurrentTopControlsShownRatio();
 }
 
 float TopControlsManager::TopControlsHeight() const {
   return client_->TopControlsHeight();
 }
 
+float TopControlsManager::BottomControlsHeight() const {
+  return client_->BottomControlsHeight();
+}
+
+float TopControlsManager::BottomControlsOffset() const {
+  return TopControlsShownRatio() * BottomControlsHeight();
+}
+
+float TopControlsManager::BottomContentOffset() const {
+  return BottomControlsHeight() - BottomControlsOffset();

[bokan, 2016/06/30 12:31:21]

This feels odd to me. When shown ratio is 0, BottomContentOffset will be
BottomControlsHeight. What does this method actually represent?

[Ian Wen, 2016/07/01 02:51:44]

Hmmm you are right. I should swap the value content-offset and controls-offset
here.

content-offset should mean "how much this bar takes on the screen now", and
controls-offset means "how much should I translate this bar". Actually I renamed
the values in the IPC message and browser side so that they make more sense.

+}
+
 void TopControlsManager::UpdateTopControlsState(TopControlsState constraints,
                                                 TopControlsState current,
                                                 bool animate) {
   DCHECK(!(constraints == SHOWN && current == HIDDEN));
   DCHECK(!(constraints == HIDDEN && current == SHOWN));
 
   permitted_state_ = constraints;
 
   // Don't do anything if it doesn't matter which state the controls are in.
   if (constraints == BOTH && current == BOTH)
@@ skipping 154 matching lines @@
   return (animation_direction_ == SHOWING_CONTROLS && new_ratio >= 1.f) ||
          (animation_direction_ == HIDING_CONTROLS && new_ratio <= 0.f);
 }
 
 void TopControlsManager::ResetBaseline() {
   accumulated_scroll_delta_ = 0.f;
   baseline_content_offset_ = ContentTopOffset();
 }
 
 }  // namespace cc