[ServiceWorkerCache] Don't handle response blobs if they don't exist

[ServiceWorkerCache] Don't handle response blobs if they don't exist

Need to add some guards.  Clearly the dispatcher needs to have tests which I hope to get to asap.

BUG=426150
Committed: https://crrev.com/01ac3bd6ad9ad0c081efaade1d5aa257a36be272
Cr-Commit-Position: refs/heads/master@{#300817}

[jkarlin, 2014-10-22 19:49:07]

jkarlin@chromium.org changed reviewers:
+ falken@chromium.org, michaeln@chromium.org

[jkarlin, 2014-10-22 19:49:07]

falken@chromium.org: Please review changes in all

michaeln@chromium.org: Please review changes in all

Thanks!

[michaeln1, 2014-10-22 20:01:20]

lgtm

[jkarlin, 2014-10-22 21:03:21]

On 2014/10/22 20:01:20, michaeln1 wrote:
> lgtm

Thanks! But can you lgtm from your other account please?

[michaeln, 2014-10-22 21:22:44]

doh, lgtm 2

[jkarlin, 2014-10-22 21:30:18]

The CQ bit was checked by jkarlin@chromium.org

[commit-bot: I haz the power, 2014-10-22 21:32:30]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/672733002/1

[commit-bot: I haz the power, 2014-10-23 00:02:26]

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

[commit-bot: I haz the power, 2014-10-23 00:02:27]

Try jobs failed on following builders:
  mac_chromium_rel on tryserver.chromium.mac
(http://build.chromium.org/p/tryserver.chromium.mac/builders/mac_chromium_rel/...)

[jsbell, 2014-10-23 00:12:30]

The CQ bit was checked by jsbell@chromium.org

[jsbell, 2014-10-23 00:13:00]

On 2014/10/23 00:02:27, I haz the power (commit-bot) wrote:
> Try jobs failed on following builders:
>   mac_chromium_rel on tryserver.chromium.mac
>
(http://build.chromium.org/p/tryserver.chromium.mac/builders/mac_chromium_rel/...)

Looks like a flake, checked the box again.

[commit-bot: I haz the power, 2014-10-23 00:13:55]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/672733002/1

[commit-bot: I haz the power, 2014-10-23 01:41:29]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2014-10-23 01:46:01]

Patchset 1 (id:??) landed as
https://crrev.com/01ac3bd6ad9ad0c081efaade1d5aa257a36be272
Cr-Commit-Position: refs/heads/master@{#300817}