mac: Fix compositing readback in content shell drt mode

For GLES2DecoderImpl::HandleResizeCHROMIUM() to have an
effect with a background surface, resize_callback_ must be set.
It's only set when by ImageTransportHelper::Initialize(), so wrap
the mesa surface with a PassThroughImageTransportSurface()
which creates an ImageTransportHelper internally.

This is also what linux does, and it makes sense that
ImageTransportSurface::CreateSurface() should have to return a
real ImageTransportSurface, not just a general GLSurface.

(See also https://codereview.chromium.org/12315103 )

BUG=111316
TEST=
webkit/tools/layout_tests/run_webkit_tests.sh --driver-name 'Content Shell' --additional-drt-flag --dump-render-tree compositing/background-color/background-color-alpha.html
passes. Most compositing/ layout tests pass.
(At least once the DRT startup crash caused by r188777 is fixed.)

Review URL: https://codereview.chromium.org/12740012

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@189143 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 5 insertions, 0 deletions

diff --git a/content/common/gpu/image_transport_surface_mac.cc b/content/common/gpu/image_transport_surface_mac.cc
index 7ebb04c..22a7460 100644
--- a/content/common/gpu/image_transport_surface_mac.cc
+++ b/content/common/gpu/image_transport_surface_mac.cc
@@ -465,6 +465,11 @@ scoped_refptr<gfx::GLSurface> ImageTransportSurface::CreateSurface(
         // baselines. So this is mostly a dummy surface.
         if (g_allow_os_mesa) {
           surface = new DRTSurfaceOSMesa();
+          if (!surface || !surface->Initialize())
+            return NULL;
+
+          surface = new PassThroughImageTransportSurface(
+              manager, stub, surface.get(), /*is_transport=*/false);
         } else {
           NOTREACHED();
           return NULL;