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

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@254514 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 254514