Fix create OnScreen surface on Mac for compositor_unittests

ui/gl/gl_surface_mac.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/gl/gl_surface.h"
 
 #include <OpenGL/CGLRenderers.h>
 
 #include "base/basictypes.h"
 #include "base/debug/trace_event.h"
@@ skipping 98 matching lines @@
 
 scoped_refptr<GLSurface> GLSurface::CreateViewGLSurface(
     gfx::AcceleratedWidget window) {
   TRACE_EVENT0("gpu", "GLSurface::CreateViewGLSurface");
   switch (GetGLImplementation()) {
     case kGLImplementationDesktopGL:
     case kGLImplementationAppleGL: {
       NOTIMPLEMENTED() << "No onscreen support on Mac.";
       return NULL;
     }
+    case kGLImplementationOSMesaGL: {
+      scoped_refptr<GLSurface> surface(new GLSurfaceOSMesaHeadless());
+      if (!surface->Initialize())
+        return NULL;
+      return surface;
+    }
     case kGLImplementationMockGL:
       return new GLSurfaceStub;
     default:
       NOTREACHED();
       return NULL;
   }
 }
 
 scoped_refptr<GLSurface> GLSurface::CreateOffscreenGLSurface(
     const gfx::Size& size) {
@@ skipping 17 matching lines @@
     }
     case kGLImplementationMockGL:
       return new GLSurfaceStub;
     default:
       NOTREACHED();
       return NULL;
   }
 }
 
 }  // namespace gfx