[android] Remove unused scroll delta in TopControls

cc/trees/layer_tree_host_impl.cc

 // Copyright 2011 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/trees/layer_tree_host_impl.h"
 
 #include <algorithm>
 #include <limits>
 
 #include "base/basictypes.h"
@@ skipping 2644 matching lines @@
         unused_root_delta.set_y(0.0f);
       // Disable overscroll on axes which is impossible to scroll.
       if (settings_.report_overscroll_only_for_scrollable_axes) {
         if (std::abs(active_tree_->TotalMaxScrollOffset().x()) <= kEpsilon ||
             !layer_impl->user_scrollable_horizontal())
           unused_root_delta.set_x(0.0f);
         if (std::abs(active_tree_->TotalMaxScrollOffset().y()) <= kEpsilon ||
             !layer_impl->user_scrollable_vertical())
           unused_root_delta.set_y(0.0f);
       }
+      if (consume_by_top_controls && unused_root_delta.y() > 0.0f)

[jdduke (slow), 2014/10/16 21:29:17]

Can you think of a solution that limits how much LTHI needs to know about the
TopControlsManager internals? For example, what if we avoid feeding the
TopControlsManager the |pending_delta| above if the root layer is at the max
limit of its scrollable area and the delta is positive? That could be folded
into the |ShouldTopControlsConsumeScroll| query.

[sujith, 2014/10/17 14:51:04]

Done.

+        top_controls_manager_->RemoveUnUsedScrollDelta(unused_root_delta.y());
     }
 
     // If the layer wasn't able to move, try the next one in the hierarchy.
     bool did_move_layer_x = std::abs(applied_delta.x()) > kEpsilon;
     bool did_move_layer_y = std::abs(applied_delta.y()) > kEpsilon;
     did_scroll_x |= did_move_layer_x;
     did_scroll_y |= did_move_layer_y;
     if (!did_move_layer_x && !did_move_layer_y) {
       // Scrolls should always bubble between the outer and inner viewports
       if (should_bubble_scrolls_ || !did_lock_scrolling_layer_ ||
@@ skipping 798 matching lines @@
 }
 
 void LayerTreeHostImpl::UnregisterPictureLayerImpl(PictureLayerImpl* layer) {
   std::vector<PictureLayerImpl*>::iterator it =
       std::find(picture_layers_.begin(), picture_layers_.end(), layer);
   DCHECK(it != picture_layers_.end());
   picture_layers_.erase(it);
 }
 
 }  // namespace cc