Clean up chrome dependencies around InstallTracker code.

      This CL prepares InstallTracker and related definitions to be moved
up to //extensions.

This is the first patch in a series of forthcoming patches to
allow non-Chrome embedders of the extension system to manage extension
installation within generic browser contexts.

BUG=398671
TBR=oshima@chromium.org for for update to //c/b/chromeos

Review URL: https://codereview.chromium.org/422063011

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@286512 0039d316-1c4b-4281-b951-d872f2087c98