chrome/installer: Make InitializeCrashReporting() return a scoped_ptr.

The idea came first while I found this code was using google_breakpad's
scoped_ptr version rather than base's version.

Then I saw in win8/ that this function could return a scoped_ptr to make
it clear the ownership to caller, i.e., this function passes the
ownership of ExceptionHandler to the caller, so it should own the
pointer to release it when it is done.

BUG=None
TEST=None
R=grt@chromium.org

Review URL: https://codereview.chromium.org/160283002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@250957 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 250957