Code: RenderWidgetHostImpl* WebContentsImpl::GetRenderWidgetHostWithPageFocus() {
  WebContentsImpl* focused_web_contents = GetFocusedWebContents();
 
   if (focused_web_contents->ShowingInterstitialPage()) {
     return static_cast<RenderFrameHostImpl*>(
               focused_web_contents->GetRenderManager()
                   ->interstitial_page()
                   ->GetMainFrame())
         ->GetRenderWidgetHost();
   }
 
  return focused_web_contents->GetMainFrame()->GetRenderWidgetHost();
}

Vulnerability Type: 
CWE ID: CWE-20
Summary: Inappropriate implementation in interstitials in Google Chrome prior to 60.0.3112.78 for Mac allowed a remote attacker to spoof the contents of the omnibox via a crafted HTML page.
Commit Message: Don't show current RenderWidgetHostView while interstitial is showing.

Also moves interstitial page tracking from RenderFrameHostManager to
WebContents, since interstitial pages are not frame-specific. This was
necessary for subframes to detect if an interstitial page is showing.

BUG=729105
TEST=See comment 13 of bug for repro steps
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_site_isolation

Review-Url: https://codereview.chromium.org/2938313002
Cr-Commit-Position: refs/heads/master@{#480117}