Allow GLSurface to indicate that it supports a specific extension.

webkit/gpu/webgraphicscontext3d_in_process_impl.cc

Index: webkit/gpu/webgraphicscontext3d_in_process_impl.cc
diff --git a/webkit/gpu/webgraphicscontext3d_in_process_impl.cc b/webkit/gpu/webgraphicscontext3d_in_process_impl.cc
index a1c8fefec7aebab418e99f370e0412fb395b28a5..89d7683c31c295b99089b7ac6fcb22e9c4d7af0c 100644
--- a/webkit/gpu/webgraphicscontext3d_in_process_impl.cc
+++ b/webkit/gpu/webgraphicscontext3d_in_process_impl.cc
@@ -335,7 +335,7 @@ void WebGraphicsContext3DInProcessImpl::prepareTexture() {
 
 void WebGraphicsContext3DInProcessImpl::postSubBufferCHROMIUM(
     int x, int y, int width, int height) {
-  DCHECK(gl_surface_->SupportsPostSubBuffer());
+  DCHECK(gl_context_->HasExtension("GL_CHROMIUM_post_sub_buffer"));
   gl_surface_->PostSubBuffer(x, y, width, height);
 }