Refactor fetch implementation in isolateserver.py.

Main changes:
  * Extract multithreaded fetch implementation from DiskCache into new
    FetchQueue class.
  * Move decompression code from IsolateServer to Storage.
  * Rearrange class order in isolateserver.py.

BUG=

DO NOT COMMIT

needs tests

Review URL: https://chromiumcodereview.appspot.com/25431003

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/swarm_client@226776 0039d316-1c4b-4281-b951-d872f2087c98
7 files changed