Telemetry: expands exception messages.

On some crashes, Telemetry were hiding useful information about the
underlying exception. Bubble it up.

BUG=310163

Review URL: https://codereview.chromium.org/34733005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@230254 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 230254