Attempt four at landing the "histogram.h removed from message_loop.h" patch.

app/animation_container_unittest.cc

Index: app/animation_container_unittest.cc
diff --git a/app/animation_container_unittest.cc b/app/animation_container_unittest.cc
index e4253c6a032029783711a3dbf069ed55bdd3d59d..d99531b1a8692d9440e491ded7a287bd83c04daf 100644
--- a/app/animation_container_unittest.cc
+++ b/app/animation_container_unittest.cc
@@ -5,6 +5,7 @@
 #include "app/animation_container.h"
 #include "app/linear_animation.h"
 #include "app/test_animation_delegate.h"
+#include "base/scoped_ptr.h"
 #include "testing/gmock/include/gmock/gmock.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
@@ -25,7 +26,7 @@ class MockObserver : public AnimationContainer::Observer {
 
 class TestAnimation : public LinearAnimation {
  public:
-  TestAnimation(AnimationDelegate* delegate)
+  explicit TestAnimation(AnimationDelegate* delegate)
       : LinearAnimation(20, 20, delegate) {
   }