Remove usages of WebContents::GetRenderViewHost().

This CL was uploaded by git cl split.

R=dfried@chromium.org

Bug: 1142671
Change-Id: Id7832e9b11000805ac8a535311254d6dda104d9c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2500491
Auto-Submit: Lucas Gadani <lfg@chromium.org>
Reviewed-by: Dana Fried <dfried@chromium.org>
Commit-Queue: Dana Fried <dfried@chromium.org>
Cr-Commit-Position: refs/heads/master@{#821165}

chrome/browser/ui/thumbnails/thumbnail_tab_helper.cc

@@ -143,7 +143,10 @@ class ThumbnailTabHelper::TabStateTracker
   // none.
   content::RenderWidgetHostView* GetView() {
     auto* const contents = web_contents();
-    return contents ? contents->GetRenderViewHost()->GetWidget()->GetView()
+    return contents ? contents->GetMainFrame()
+                          ->GetRenderViewHost()
+                          ->GetWidget()
+                          ->GetView()
                     : nullptr;
   }