Remove usages of WebContents::GetRenderViewHost().

This CL was uploaded by git cl split.

R=falken@chromium.org

Bug: 1142671
Change-Id: Ie6c1889b3eff87c5c7edb4071f31767be2c8a1fd
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2500614
Auto-Submit: Lucas Gadani <lfg@chromium.org>
Reviewed-by: Matt Falkenhagen <falken@chromium.org>
Commit-Queue: Matt Falkenhagen <falken@chromium.org>
Cr-Commit-Position: refs/heads/master@{#821082}

components/prerender/browser/prerender_contents.cc

@@ -550,8 +550,9 @@ std::unique_ptr<WebContents> PrerenderContents::ReleasePrerenderContents() {
 }
 
 RenderViewHost* PrerenderContents::GetRenderViewHost() {
-  return prerender_contents_ ? prerender_contents_->GetRenderViewHost()
-                             : nullptr;
+  return prerender_contents_
+             ? prerender_contents_->GetMainFrame()->GetRenderViewHost()
+             : nullptr;
 }
 
 std::unique_ptr<base::DictionaryValue> PrerenderContents::GetAsValue() const {