Remove usages of WebContents::GetRenderViewHost().

This CL was uploaded by git cl split.

R=caseq@chromium.org

Bug: 1142671
Change-Id: Iade09088b5a7da8fb5bc0604facb2e0f9cb63218
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2500496
Auto-Submit: Lucas Gadani <lfg@chromium.org>
Reviewed-by: Andrey Kosyakov <caseq@chromium.org>
Commit-Queue: Andrey Kosyakov <caseq@chromium.org>
Cr-Commit-Position: refs/heads/master@{#821088}

headless/lib/browser/headless_web_contents_impl.cc

@@ -90,7 +90,7 @@ class HeadlessWebContentsImpl::Delegate : public content::WebContentsDelegate {
   }
 
   void ActivateContents(content::WebContents* contents) override {
-    contents->GetRenderViewHost()->GetWidget()->Focus();
+    contents->GetMainFrame()->GetRenderViewHost()->GetWidget()->Focus();
   }
 
   void CloseContents(content::WebContents* source) override {