[Telemetry] Fix printing of SyntaxErrors.

Also, display up to 1024 characters of local variable contents. Some messages on
the bots were too truncated to be useful.

BUG=323452

Review URL: https://codereview.chromium.org/95403003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@238008 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 238008