aura: Clean up compositor initialization/destruction.

ash/test/ash_test_helper.cc

Index: ash/test/ash_test_helper.cc
diff --git a/ash/test/ash_test_helper.cc b/ash/test/ash_test_helper.cc
index 84d28c5210fa99289b17e808c4ef3370b0d4bdaa..65ed8748b560c311a4d1bd3f7a445ac9eba979ae 100644
--- a/ash/test/ash_test_helper.cc
+++ b/ash/test/ash_test_helper.cc
@@ -13,6 +13,7 @@
 #include "base/run_loop.h"
 #include "ui/aura/env.h"
 #include "ui/base/ime/input_method_initializer.h"
+#include "ui/compositor/compositor.h"
 #include "ui/compositor/scoped_animation_duration_scale_mode.h"
 #include "ui/message_center/message_center.h"
 
@@ -60,6 +61,10 @@ void AshTestHelper::SetUp() {
   }
 #endif
 
+  // The ContextFactory must exist before any Compositors are created.
+  bool allow_test_contexts = true;
+  ui::Compositor::InitializeContextFactoryForTests(allow_test_contexts);
+
   ash::Shell::CreateInstance(test_shell_delegate_);
   Shell* shell = Shell::GetInstance();
   test_shell_delegate_->test_session_state_delegate()->