[chromedriver] Add a separate command for the heap snapshot.

BUG=

Review URL: https://codereview.chromium.org/46443002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@231439 0039d316-1c4b-4281-b951-d872f2087c98
4 files changed