Revert 254514 "Revert 254507 "Reland "Move WebKitPlatformSupport..."

This builds locally and on CQ. Relanding and will keep an eye out on bots, and clobber if necessary.

> Revert 254507 "Reland "Move WebKitPlatformSupportImpl over to co..."
> 
> > Reland "Move WebKitPlatformSupportImpl over to content."
> > 
> > In the process rename it BlinkPlatformImpl to avoid conflicts and
> > confusion with an existing WebKitPlatformSupportImpl class in content.
> > 
> > This step is necessary because WebKitPlatformSupportImpl uses
> > webkit/common/user_agent/, and we also want to move user_agent to
> > content.
> > 
> > So this needs to happen first because webkit can't depend on content as
> > content already depends on webkit, otherwise we would be creating a
> > circular dependency.
> > 
> > WebURLLoader and WebSocketStreamHandleImpl had to be moved with
> > WebKitPlatformSupportImpl, because they both uses
> > WebKitPlatformSupportImpl and vice-versa.
> > 
> > BUG=265753, 338338, 237249
> > TEST=content_unittests
> > R=jam@chromium.org
> > TBR=darin
> > 
> > Review URL: https://codereview.chromium.org/180153012
> 
> TBR=tfarina@chromium.org
> 
> Review URL: https://codereview.chromium.org/180383006

TBR=stgao@chromium.org

Review URL: https://codereview.chromium.org/186363002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@254641 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 254641