Fixes bisect-perf-regression.py for "special" metrics.

Metrics may have regexp characters requiring escaping, such as:
ImageDecoding_avg_by_url/image_decoding.html?gif

Example of the fix:
http://chromeperf79.chrome.corp.google.com:8028/builders/linux_bisect/builds/185

BUG=233580

Review URL: https://chromiumcodereview.appspot.com/14772033

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@200063 0039d316-1c4b-4281-b951-d872f2087c98
1 file changed