Add the viewer toolbar to the PDF extension.

BUG=303491
R=arv@chromium.org, ganetsky@chromium.org

Review URL: https://codereview.chromium.org/110723007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@247578 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 247578