Service Workers: CacheStorage should reject on error, not resolve

Change a couple of `resolve()` calls to `reject()`. Tests pending.

TEST=https://codereview.chromium.org/430993002
R=gavinp@chromium.org
BUG=408365

Review URL: https://codereview.chromium.org/516073002

git-svn-id: svn://svn.chromium.org/blink/trunk@181105 bbb929c8-8fbe-4397-9dbb-9b2b20218538