Fix flakyness in NavigateRemoteFrame browsertest.

content/renderer/render_frame_proxy.cc

Index: content/renderer/render_frame_proxy.cc
diff --git a/content/renderer/render_frame_proxy.cc b/content/renderer/render_frame_proxy.cc
index 5af5f570fc8c0c946b22c1be6f96df2904087efe..0253b961f8ce52442f39c6d452cea07071cd3b13 100644
--- a/content/renderer/render_frame_proxy.cc
+++ b/content/renderer/render_frame_proxy.cc
@@ -195,6 +195,13 @@ void RenderFrameProxy::OnChildFrameProcessGone() {
 }
 
 void RenderFrameProxy::OnCompositorFrameSwapped(const IPC::Message& message) {
+  // If this WebFrame has already been detached, its parent will be null. This
+  // can happen when swapping a WebRemoteFrame with a WebLocalFrame, where this
+  // message may arrive after the frame was removed from the frame tree, but
+  // before the frame has been destroyed. http://crbug.com/446575.
+  if (!web_frame()->parent())
+    return;
+
   FrameMsg_CompositorFrameSwapped::Param param;
   if (!FrameMsg_CompositorFrameSwapped::Read(&message, &param))
     return;