aura: use TestWebGraphicsContext3D for the shared contexts

ui/compositor/test_web_graphics_context_3d.h

Index: ui/compositor/test_web_graphics_context_3d.h
diff --git a/ui/compositor/test_web_graphics_context_3d.h b/ui/compositor/test_web_graphics_context_3d.h
index dcf92f05a2a9dfd9ae7f65f120c5eb6af9088178..517245a4f482b8d24bbb59b9d46c0b996565f610 100644
--- a/ui/compositor/test_web_graphics_context_3d.h
+++ b/ui/compositor/test_web_graphics_context_3d.h
@@ -9,6 +9,7 @@
 #include "base/memory/ref_counted.h"
 #include "third_party/WebKit/Source/WebKit/chromium/public/platform/WebGraphicsContext3D.h"
 #include "third_party/WebKit/Source/WebKit/chromium/public/platform/WebString.h"
+#include "ui/compositor/compositor_export.h"
 
 namespace gfx {
 class GLContext;
@@ -18,7 +19,8 @@ class GLSurface;
 namespace ui {
 
 // WebGraphicsContext3D that does nothing. Suitable for testing.
-class TestWebGraphicsContext3D : public WebKit::WebGraphicsContext3D {
+class COMPOSITOR_EXPORT TestWebGraphicsContext3D :
+    public NON_EXPORTED_BASE(WebKit::WebGraphicsContext3D) {
  public:
   TestWebGraphicsContext3D();
   virtual ~TestWebGraphicsContext3D();