[ChromeDriver] Use chromium snapshots for Linux_64 and Mac.

For blink snapshots of Linux_64 and Mac, their last update was 2014-06-19.

TBR=samuong

Review URL: https://codereview.chromium.org/353773006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@279758 0039d316-1c4b-4281-b951-d872f2087c98