Update HeapSnapshotTaker to catch up with recent changes to the remote debugging protocol

After https://codereview.chromium.org/98273008/ is landed heap snapshot will be sent to the frontend immeiately in response to HeapProfiler.takeHeapSnapshot command. This change switches HeapSnapshotTaker to the new protocol.

BUG=324769

Review URL: https://codereview.chromium.org/149093005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@250650 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 250650