[Fetch] Request constructor should reflect body consumption.

[Fetch] Request constructor should reflect body consumption.

As discussed at [1], new Request(req) should generate a Request object
having body that was unconsumed at the calling time.

1: https://github.com/slightlyoff/ServiceWorker/issues/452

BUG=472931
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=193069

[yhirano, 2015-04-02 02:35:10]

The CQ bit was checked by yhirano@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2015-04-02 02:35:57]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1056783002/1

[commit-bot: I haz the power, 2015-04-02 02:42:12]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-04-02 02:42:14]

Try jobs failed on following builders:
  mac_blink_compile_dbg on tryserver.blink (JOB_FAILED,
http://build.chromium.org/p/tryserver.blink/builders/mac_blink_compile_dbg/bu...)

[yhirano, 2015-04-02 04:32:25]

yhirano@chromium.org changed reviewers:
+ horo@chromium.org

[yhirano, 2015-04-02 04:32:26]

This CL depends on https://codereview.chromium.org/1049983003/.

[horo, 2015-04-02 07:19:15]

lgtm

[yhirano, 2015-04-03 00:09:12]

The CQ bit was checked by yhirano@chromium.org

[commit-bot: I haz the power, 2015-04-03 00:10:44]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1056783002/20001

[commit-bot: I haz the power, 2015-04-03 03:49:28]

Committed patchset #2 (id:20001) as
https://src.chromium.org/viewvc/blink?view=rev&revision=193069