[#6]Pass gfx structs by const ref (gfx::Vector2d)

cc/trees/layer_tree_host_unittest_scroll.cc

Index: cc/trees/layer_tree_host_unittest_scroll.cc
diff --git a/cc/trees/layer_tree_host_unittest_scroll.cc b/cc/trees/layer_tree_host_unittest_scroll.cc
index 387115456366ee806b8140737062722fb4273c79..37178b7f167078b03b15cae20f34084038add137 100644
--- a/cc/trees/layer_tree_host_unittest_scroll.cc
+++ b/cc/trees/layer_tree_host_unittest_scroll.cc
@@ -72,7 +72,7 @@ class LayerTreeHostScrollTestScrollSimple : public LayerTreeHostScrollTest {
     }
   }
 
-  virtual void ApplyScrollAndScale(gfx::Vector2d scroll_delta,
+  virtual void ApplyScrollAndScale(const gfx::Vector2d& scroll_delta,
                                    float scale) OVERRIDE {
     num_scrolls_++;
   }
@@ -309,7 +309,7 @@ class LayerTreeHostScrollTestScrollAbortedCommit
     }
   }
 
-  virtual void ApplyScrollAndScale(gfx::Vector2d scroll_delta,
+  virtual void ApplyScrollAndScale(const gfx::Vector2d& scroll_delta,
                                    float scale) OVERRIDE {
     num_impl_scrolls_++;
   }
@@ -465,7 +465,7 @@ class LayerTreeHostScrollTestCaseWithChild : public LayerTreeHostScrollTest {
     final_scroll_offset_ = expected_scroll_layer_->scroll_offset();
   }
 
-  virtual void ApplyScrollAndScale(gfx::Vector2d scroll_delta,
+  virtual void ApplyScrollAndScale(const gfx::Vector2d& scroll_delta,
                                    float scale) OVERRIDE {
     num_scrolls_++;
   }
@@ -805,7 +805,7 @@ class ImplSidePaintingScrollTestSimple : public ImplSidePaintingScrollTest {
     }
   }
 
-  virtual void ApplyScrollAndScale(gfx::Vector2d scroll_delta,
+  virtual void ApplyScrollAndScale(const gfx::Vector2d& scroll_delta,
                                    float scale) OVERRIDE {
     num_scrolls_++;
   }