Don't calculate a shown ratio when top controls height is 0.

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 <algorithm>
 
 #include "base/logging.h"
 #include "cc/animation/keyframed_animation_curve.h"
@@ skipping 86 matching lines @@
   DCHECK(!pinch_gesture_active_);
   ResetAnimations();
   ResetBaseline();
 }
 
 gfx::Vector2dF TopControlsManager::ScrollBy(
     const gfx::Vector2dF& pending_delta) {
   if (pinch_gesture_active_)
     return pending_delta;
 
+  if (!TopControlsHeight())
+    return pending_delta;
+
   if (permitted_state_ == SHOWN && pending_delta.y() > 0)
     return pending_delta;
   else if (permitted_state_ == HIDDEN && pending_delta.y() < 0)
     return pending_delta;
 
   accumulated_scroll_delta_ += pending_delta.y();
 
   float old_offset = ContentTopOffset();
   client_->SetCurrentTopControlsShownRatio(
       (baseline_content_offset_ - accumulated_scroll_delta_) /
@@ skipping 108 matching lines @@
   }
   return false;
 }
 
 void TopControlsManager::ResetBaseline() {
   accumulated_scroll_delta_ = 0.f;
   baseline_content_offset_ = ContentTopOffset();
 }
 
 }  // namespace cc