Fix end_to_end_test performance regression caused by using mutexes
instead of notifications in server_thread. Testing only.

Merge internal change: 59322530

Reversed pause/resume changes of server_thread in the following CL:
https://codereview.chromium.org/127503002/

R=rch@chromium.org

Review URL: https://codereview.chromium.org/132073002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@243948 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 243948