Some simplifications, as a pre-step to http://crbug.com/40103

      - simplify the y geolocation IPC protocol, by using the error code already in Geoposition
- convert Geoposition's error_message to UTF8 as this is easier alround
- simplify the dispatcher host render id set (as the process_id part is implicit from the dispatcher host instance)

BUG=40103
TEST=unit_tests --gtest_filter=*Geol*

Review URL: http://codereview.chromium.org/2648002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@49060 0039d316-1c4b-4281-b951-d872f2087c98