Creating a child frame results in the RenderFrame initializing (and creating RenderFrameObservers) before the LocalFrame has been created. That doesn't happen when creating the main frame or provisional frames.

Today's CreateChildFrame:

LocalFrameClientImpl::CreateFrame
  . WebLocalFrameImpl::CreateChildFrame
    . RenderFrameImpl::CreateChildFrame
      . child_render_frame->Initialize
    . child_web_local_frame->InitializeCoreFrame


I propose that we create a new WebFrameClient::InitializeFrame function so that we have the following:

LocalFrameClientImpl::CreateFrame
  . WebLocalFrameImpl::CreateChildFrame
    . RenderFrameImpl::CreateChildFrame
    . child_web_local_frame->InitializeCoreFrame()
    . child_client->InitializeFrame()