Inform webkit when PPAPI plugin contents are opaque.

content/renderer/pepper/pepper_platform_context_3d_impl.cc

Index: content/renderer/pepper/pepper_platform_context_3d_impl.cc
diff --git a/content/renderer/pepper/pepper_platform_context_3d_impl.cc b/content/renderer/pepper/pepper_platform_context_3d_impl.cc
index c16003c1add9695c92fd531fa2423c818ef7b168..812483dba063e3c92e3cb57951232152c26a14cd 100644
--- a/content/renderer/pepper/pepper_platform_context_3d_impl.cc
+++ b/content/renderer/pepper/pepper_platform_context_3d_impl.cc
@@ -21,6 +21,7 @@ PlatformContext3DImpl::PlatformContext3DImpl(
     PepperParentContextProvider* parent_context_provider)
       : parent_context_provider_(parent_context_provider),
         parent_texture_id_(0),
+        has_alpha_(false),
         command_buffer_(NULL),
         weak_ptr_factory_(ALLOW_THIS_IN_INITIALIZER_LIST(this)) {
 }
@@ -98,6 +99,9 @@ bool PlatformContext3DImpl::Init(const int32* attrib_list) {
         case ContentGLContext::HEIGHT:
           surface_size.set_height(attr[1]);
           break;
+        case ContentGLContext::ALPHA_SIZE:
+          has_alpha_ = attr[1] > 0;
+        // fall-through
         default:
           attribs.push_back(attr[0]);
           attribs.push_back(attr[1]);
@@ -152,6 +156,11 @@ unsigned PlatformContext3DImpl::GetBackingTextureId() {
   return parent_texture_id_;
 }
 
+bool PlatformContext3DImpl::IsOpaque() {
+  DCHECK(command_buffer_);
+  return !has_alpha_;
+}
+
 gpu::CommandBuffer* PlatformContext3DImpl::GetCommandBuffer() {
   return command_buffer_;
 }