cc: Use the correct internal format for glCopyTexImage2D calls.

blimp/client/feature/compositor/blimp_context_provider.cc

Index: blimp/client/feature/compositor/blimp_context_provider.cc
diff --git a/blimp/client/feature/compositor/blimp_context_provider.cc b/blimp/client/feature/compositor/blimp_context_provider.cc
index 07e94e8e437bca8ccaa4ca1ae9a95f26b3a47bb7..a4699fee8df78e35740827ae02aaf4fde7c0878f 100644
--- a/blimp/client/feature/compositor/blimp_context_provider.cc
+++ b/blimp/client/feature/compositor/blimp_context_provider.cc
@@ -124,5 +124,11 @@ void BlimpContextProvider::OnLostContext() {
     gr_context_->OnLostContext();
 }
 
+uint32_t BlimpContextProvider::GetCopyTextureInternalFormat() {
+  // The attributes used to create the context in the constructor specify
+  // an alpha channel.
+  return GL_RGBA;
+}
+
 }  // namespace client
 }  // namespace blimp