Specify a file size limit for minidumps

When there are upwards of 200 threads in a crashing process, each having an
8KB stack, this can result in a huge, 1.8MB minidump file.  The Crash Server
throws away any uploaded file larger than 1.2MB.  Setting the minidump size
limit (see https://breakpad.appspot.com/487002/) will result in less stack
being dumped when there are so many threads.

BUG=chromium-os:31447, chromium:154546

Contributed by Michael Krebs <mkrebs@chromium.org>

Review URL: https://chromiumcodereview.appspot.com/11142010

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@169221 0039d316-1c4b-4281-b951-d872f2087c98