Revise DCHECK to consider app-guest WeContents difference.

This CL revises a DCHECK that has been firing (erroneously) when Flash
content is loaded inside a WebView.

Bug: 873672
Change-Id: I75c12c67b47a5b337054a262991d23247bbbb4ea
Reviewed-on: https://chromium-review.googlesource.com/1173359Reviewed-by: Ehsan Karamad <ekaramad@chromium.org>
Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
Commit-Queue: James MacLean <wjmaclean@chromium.org>
Cr-Commit-Position: refs/heads/master@{#583232}

extensions/browser/app_window/app_window.cc

@@ -351,8 +351,13 @@ bool AppWindow::CheckMediaAccessPermission(
     content::RenderFrameHost* render_frame_host,
     const GURL& security_origin,
     content::MediaStreamType type) {
-  DCHECK_EQ(AppWindow::web_contents(),
-            content::WebContents::FromRenderFrameHost(render_frame_host));
+  DCHECK(AppWindow::web_contents() ==
+             content::WebContents::FromRenderFrameHost(render_frame_host) ||
+         (content::WebContents::FromRenderFrameHost(render_frame_host)
+              ->GetOuterWebContents() &&
+          AppWindow::web_contents() ==
+              content::WebContents::FromRenderFrameHost(render_frame_host)
+                  ->GetOuterWebContents()));
   return helper_->CheckMediaAccessPermission(render_frame_host, security_origin,
                                              type);
 }