Revert 167830 "Refactor WebHelperPluginImpl to simplify plugin c..."

This broke the Android dbg builder compile.

> Refactor WebHelperPluginImpl to simplify plugin creation.
> 
> As it turns out, it's not necessary to create a Page, or even a WebFrame
> at all. This was problematic for the current work to move embedder
> functionality from WebViewClient to WebFrameClient since it entangled
> two WebFrames with the same WebFrameClient.
> 
> A bonus side effect is the code gets a lot simpler: WebHelperPlugin will
> no longer needs to be a WebWidget, and it doesn't need to carefully
> construct and destruct its internal state. This allows logic specific to
> WebHelperPlugin to be completely removed from WebView.
> 
> After this change rolls into Chrome, WebHelperPlugin will be completely
> removed from the embedding API, as Chrome no longer needs to interact
> with it at all.
> 
> BUG=346543
> R=abarth@chromium.org, ddorwin@chromium.org
> 
> Review URL: https://codereview.chromium.org/175593008

TBR=dcheng@chromium.org

Review URL: https://codereview.chromium.org/179973005

git-svn-id: svn://svn.chromium.org/blink/trunk@167832 bbb929c8-8fbe-4397-9dbb-9b2b20218538