Reland 249382 "Remove references to WebContents from PasswordFormManager."

> Revert "Remove references to WebContents from PasswordFormManager."
> 
> This reverts commit r249382.
> 
> It's unclear what broke the tree and I'm trying this revert in the hopes
> of finding the problem.

TBR=agl@chromium.org

Review URL: https://codereview.chromium.org/132503008

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@249418 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 249418