Avoid unnecessary gloweffect calls

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 2254 matching lines @@
     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_ ||
           layer_impl == OuterViewportScrollLayer())
         continue;
       else
         break;
     }
 
     if (layer_impl == InnerViewportScrollLayer())

[aelias_OOO_until_Jul13, 2014/03/21 00:16:11]

Replace this with:

    if (layer_impl == InnerViewportScrollLayer()) {
      unused_root_delta.Subtract(applied_delta);
      const float kOverscrollEpsilon = 0.01f;
      if (fabs(unused_root_delta.x()) < kOverscrollEpsilon)
        unused_root_delta.set_x(0.0f);
      if (fabs(unused_root_delta.y()) < kOverscrollEpsilon)
        unused_root_delta.set_y(0.0f);
    }

(I observe the error values get as high as 0.002f so 0.01f seems like a
reasonable epsilon value.)

       unused_root_delta.Subtract(applied_delta);
 
     did_lock_scrolling_layer_ = true;
     if (!should_bubble_scrolls_) {
       active_tree_->SetCurrentlyScrollingLayer(layer_impl);
       break;
     }
 
     // If the applied delta is within 45 degrees of the input delta, bail out to
     // make it easier to scroll just one layer in one direction without
@@ skipping 21 matching lines @@
     client_->RenewTreePriority();
   }
 
   // Scrolling along an axis resets accumulated root overscroll for that axis.
   if (did_scroll_x)
     accumulated_root_overscroll_.set_x(0);
   if (did_scroll_y)
     accumulated_root_overscroll_.set_y(0);
 
   accumulated_root_overscroll_ += unused_root_delta;
+
+  // Scrolling along an axis resets unused root delta which unnecessarily calls
+  // glow effect

[danakj, 2014/03/20 17:01:30]

nit: missing period

+  if (did_scroll_x)
+    unused_root_delta.set_y(0);
+  if (did_scroll_y)
+    unused_root_delta.set_x(0);
+
   bool did_overscroll = !gfx::ToRoundedVector2d(unused_root_delta).IsZero();

[aelias_OOO_until_Jul13, 2014/03/21 00:16:11]

And this can be simplified to:

bool did_overscroll = !unused_root_delta.IsZero();

   if (did_overscroll && input_handler_client_) {
     DidOverscrollParams params;
     params.accumulated_overscroll = accumulated_root_overscroll_;
     params.latest_overscroll_delta = unused_root_delta;
     params.current_fling_velocity = current_fling_velocity_;
     input_handler_client_->DidOverscroll(params);
   }
 
   return did_scroll_content || did_scroll_top_controls;
 }
@@ skipping 692 matching lines @@
   swap_promise_monitor_.erase(monitor);
 }
 
 void LayerTreeHostImpl::NotifySwapPromiseMonitorsOfSetNeedsRedraw() {
   std::set<SwapPromiseMonitor*>::iterator it = swap_promise_monitor_.begin();
   for (; it != swap_promise_monitor_.end(); it++)
     (*it)->OnSetNeedsRedrawOnImpl();
 }
 
 }  // namespace cc