Add create WGC3DInProcessCommandBuffer for on-screen context

cc/test/pixel_test.cc

Index: cc/test/pixel_test.cc
diff --git a/cc/test/pixel_test.cc b/cc/test/pixel_test.cc
index 8d0e64e844d051aa84a6a3bd6c4b7a6f2bcbdf20..8563440aa789dc00b68151fdb86e8e6bd8ef5c96 100644
--- a/cc/test/pixel_test.cc
+++ b/cc/test/pixel_test.cc
@@ -57,10 +57,10 @@ PixelTest::~PixelTest() {}
 void PixelTest::SetUp() {
   CHECK(gfx::InitializeGLBindings(gfx::kGLImplementationOSMesaGL));
 
-  scoped_ptr<webkit::gpu::WebGraphicsContext3DInProcessCommandBufferImpl>
-      context3d(
-          new webkit::gpu::WebGraphicsContext3DInProcessCommandBufferImpl(
-              WebKit::WebGraphicsContext3D::Attributes()));
+  using webkit::gpu::WebGraphicsContext3DInProcessCommandBufferImpl;
+  scoped_ptr<WebGraphicsContext3DInProcessCommandBufferImpl> context3d(
+      WebGraphicsContext3DInProcessCommandBufferImpl::CreateOffscreenContext(
+          WebKit::WebGraphicsContext3D::Attributes()));
   output_surface_.reset(new OutputSurface(
       context3d.PassAs<WebKit::WebGraphicsContext3D>()));
   resource_provider_ = ResourceProvider::Create(output_surface_.get(), 0);