aura: Set up the mock compositor to get gfx_unittests green on linux.

ui/gfx/test_suite.cc

Index: ui/gfx/test_suite.cc
diff --git a/ui/gfx/test_suite.cc b/ui/gfx/test_suite.cc
index 1901ed003f69e1f4b28788244d532acc96dc0492..baa820da7407ccfc2a03176292296307c8af9ab1 100644
--- a/ui/gfx/test_suite.cc
+++ b/ui/gfx/test_suite.cc
@@ -15,6 +15,10 @@
 #include "base/mac/foundation_util.h"
 #endif
 
+#if defined(USE_AURA)
+#include "ui/gfx/compositor/compositor_test_support.h"
+#endif
+
 GfxTestSuite::GfxTestSuite(int argc, char** argv) : TestSuite(argc, argv) {}
 
 void GfxTestSuite::Initialize() {
@@ -50,6 +54,11 @@ void GfxTestSuite::Initialize() {
   // Force unittests to run using en-US so if we test against string
   // output, it'll pass regardless of the system language.
   ui::ResourceBundle::InitSharedInstance("en-US");
+
+#if defined(USE_AURA)
+  ui::CompositorTestSupport::Initialize();
+  ui::CompositorTestSupport::SetupMockCompositor();
+#endif
 }
 
 void GfxTestSuite::Shutdown() {