[Telemetry] Provide a better exception when app crashes on Android.

Instead of getting index oob, now you get a more helpful assertion.

BUG=
R=bulach@chromium.org

Review URL: https://codereview.chromium.org/24467002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@225288 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 225288