[#5] Pass gfx structs by const ref (gfx::Vector2dF)

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 2051 matching lines @@
     UMA_HISTOGRAM_BOOLEAN("TryScroll.SlowScroll", false);
     return ScrollStarted;
   }
   return ScrollIgnored;
 }
 
 gfx::Vector2dF LayerTreeHostImpl::ScrollLayerWithViewportSpaceDelta(
     LayerImpl* layer_impl,
     float scale_from_viewport_to_screen_space,
     const gfx::PointF& viewport_point,
-    gfx::Vector2dF viewport_delta) {
+    const gfx::Vector2dF& viewport_delta) {
   // Layers with non-invertible screen space transforms should not have passed
   // the scroll hit test in the first place.
   DCHECK(layer_impl->screen_space_transform().IsInvertible());
   gfx::Transform inverse_screen_space_transform(
       gfx::Transform::kSkipInitialization);
   bool did_invert = layer_impl->screen_space_transform().GetInverse(
       &inverse_screen_space_transform);
   // TODO(shawnsingh): With the advent of impl-side crolling for non-root
   // layers, we may need to explicitly handle uninvertible transforms here.
   DCHECK(did_invert);
@@ skipping 52 matching lines @@
   DCHECK(!end_clipped);
   if (end_clipped)
     return gfx::Vector2dF();
   gfx::PointF actual_viewport_end_point =
       gfx::ScalePoint(actual_screen_space_end_point,
                       1.f / scale_from_viewport_to_screen_space);
   return actual_viewport_end_point - viewport_point;
 }
 
 static gfx::Vector2dF ScrollLayerWithLocalDelta(LayerImpl* layer_impl,
-                                                gfx::Vector2dF local_delta) {
+    const gfx::Vector2dF& local_delta) {
   gfx::Vector2dF previous_delta(layer_impl->ScrollDelta());
   layer_impl->ScrollBy(local_delta);
   return layer_impl->ScrollDelta() - previous_delta;
 }
 
 bool LayerTreeHostImpl::ScrollBy(gfx::Point viewport_point,
-                                 gfx::Vector2dF scroll_delta) {
+                                 const gfx::Vector2dF& scroll_delta) {
   TRACE_EVENT0("cc", "LayerTreeHostImpl::ScrollBy");
   if (!CurrentlyScrollingLayer())
     return false;
 
   gfx::Vector2dF pending_delta = scroll_delta;
   gfx::Vector2dF unused_root_delta;
   bool did_scroll_x = false;
   bool did_scroll_y = false;
   bool consume_by_top_controls = top_controls_manager_ &&
       (scroll_delta.y() < 0 ||
@@ skipping 180 matching lines @@
   if (!wheel_scrolling_) {
     // Allow the fling to lock to the first layer that moves after the initial
     // fling |ScrollBy()| event.
     did_lock_scrolling_layer_ = false;
     should_bubble_scrolls_ = false;
   }
 
   return ScrollStarted;
 }
 
-void LayerTreeHostImpl::NotifyCurrentFlingVelocity(gfx::Vector2dF velocity) {
+void LayerTreeHostImpl::NotifyCurrentFlingVelocity(
+    const gfx::Vector2dF& velocity) {
   current_fling_velocity_ = velocity;
 }
 
 float LayerTreeHostImpl::DeviceSpaceDistanceToLayer(
     const gfx::PointF& device_viewport_point,
     LayerImpl* layer_impl) {
   if (!layer_impl)
     return std::numeric_limits<float>::max();
 
   gfx::Rect layer_impl_bounds(
@@ skipping 557 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