Remove some WebContents::GetRenderViewHost() calls.

web_contents->GetRenderViewHost()->GetProcess() becomes
web_contents->GetMainFrame()->GetProcess() unless the call is part of a
process id + routing id pair.

Also remove an obsolete RenderViewGone reference in
background_printing_manager.cc.

BUG=666525

Review-Url: https://codereview.chromium.org/2527133002
Cr-Commit-Position: refs/heads/master@{#435358}
10 files changed