Don't expose URL.createObjectURL and revokeObjectURL to Service Workers

Per FileAPI[1] which was updated based on Service Worker discussion[2],
minting blob URLs should not be possible within SWs.

A bug has been filed against MediaSource[3] to update the IDL there
(following the same logic), and mediastream's createObjectURL is no
longer present in the standard. Regardless, the overloads should
never execute in Service Workers as those types (MediaStream,
MediaSource) are not exposed in that context.

Note that the [Exposed] attributes are applied directly to the
interface members as they appear to be ignored on the partial
interface. (Bug?)

[1] https://w3c.github.io/FileAPI/#creating-revoking
[2] https://github.com/slightlyoff/ServiceWorker/issues/688
[3] https://github.com/w3c/media-source/issues/67

Intent Thread: https://groups.google.com/a/chromium.org/d/msg/blink-dev/HuA7Ng9U0oc/CYvfMoeyBwAJ

BUG=604951,608460

Review-Url: https://codereview.chromium.org/1908263002
Cr-Commit-Position: refs/heads/master@{#393271}
11 files changed