Allow MimeHandlerViewGuest be embedded inside OOPIFs

content/public/browser/browser_plugin_guest_delegate.cc

Index: content/public/browser/browser_plugin_guest_delegate.cc
diff --git a/content/public/browser/browser_plugin_guest_delegate.cc b/content/public/browser/browser_plugin_guest_delegate.cc
index 732df238f91431509e6f998d56cc1508e9a0bdf3..affcdfb858bc3d8f53e3c7ed58d2757b23509354 100644
--- a/content/public/browser/browser_plugin_guest_delegate.cc
+++ b/content/public/browser/browser_plugin_guest_delegate.cc
@@ -36,4 +36,10 @@ bool BrowserPluginGuestDelegate::CanUseCrossProcessFrames() {
   return true;
 }
 
+RenderFrameHost* BrowserPluginGuestDelegate::GetEmbedderFrame() {
+  if (GetOwnerWebContents())
+    return GetOwnerWebContents()->GetMainFrame();
+  return nullptr;
+}
+
 }  // namespace content