IndexedDB: Added IDBIndex.getAll() implementation.
This is the experimental IDBIndex.getAll implementation for
retrieving multiple values in a single request as proposed in
https://www.w3.org/2008/webapps/wiki/IndexedDatabaseFeatures
Mozilla's documentation for IDBIndex.getAll is at:
https://developer.mozilla.org/en-US/docs/Web/API/IDBIndex/getAll
In order to use run Chrome with: --enable-experimental-web-platform-features
BUG=457450
Review URL: https://codereview.chromium.org/
1147433002
Cr-Commit-Position: refs/heads/master@{#330631}