Service Workers/Fetch: Fix Response constructor for empty/null

Service Workers/Fetch: Fix Response constructor for empty/null

The fetch spec[1] has the body parameter of the Response constructor
marked optional, and none of the accepted types are nullable. In contrast,
the Blink implementation supported passing null but required an argument.
Make the impl match the spec.

[1] https://fetch.spec.whatwg.org

BUG=412027
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=185051

[jsbell, 2014-11-07 21:31:17]

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

[jsbell, 2014-11-07 21:31:18]

horo@ - please take a look?

[horo, 2014-11-10 01:34:44]

lgtm
Thank you!

[jsbell, 2014-11-10 17:55:16]

The CQ bit was checked by jsbell@chromium.org

[commit-bot: I haz the power, 2014-11-10 17:55:46]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/701683005/1

[commit-bot: I haz the power, 2014-11-10 17:57:40]

Committed patchset #1 (id:1) as 185051