Fix up compositor mocking.

ui/gfx/compositor/test_compositor.h

Index: ui/gfx/compositor/test_compositor.h
diff --git a/ui/gfx/compositor/test_compositor.h b/ui/gfx/compositor/test_compositor.h
index 647249664e765faeca6457ac4a369d3df11d392d..43093fa288a92c27b367c1c3f072e70db05b3918 100644
--- a/ui/gfx/compositor/test_compositor.h
+++ b/ui/gfx/compositor/test_compositor.h
@@ -10,13 +10,14 @@
 #include "base/memory/scoped_ptr.h"
 #include "base/compiler_specific.h"
 #include "ui/gfx/compositor/compositor.h"
+#include "ui/gfx/compositor/compositor_export.h"
 
 namespace ui {
 
 class TestCompositorDelegate;
 
 // Trivial Compositor implementation that creates Textures of type TestTexture.
-class TestCompositor : public ui::Compositor {
+class COMPOSITOR_EXPORT TestCompositor : public ui::Compositor {
  public:
   explicit TestCompositor(CompositorDelegate* owner);
   virtual ~TestCompositor();
@@ -31,6 +32,10 @@ class TestCompositor : public ui::Compositor {
   // A simple factory that creates a test compositor with a given delegate
   static ui::Compositor* Create(ui::CompositorDelegate* owner);
 
+  // Called by tests that want to use a mocked compositor.
+  // Implementation is no-oped on platforms that don't use a compositor.
+  static void SetupTestCompositor();
+
  protected:
   virtual void OnWidgetSizeChanged() OVERRIDE;