ServiceWorker CacheID update
Previous design:
1. The renderer needed all references to the same ServiceWorekrCache* to have the same CacheID.
2. The renderer would only send an IPC that a CacheID was deleted when the last reference to the CacheID was deleted in javascript.
After https://codereview.chromium.org/
474593002/ and https://codereview.chromium.org/
433793002/:
1. The renderer doesn't need all references to the same ServiceWorkerCache* to have the same CacheID.
2. The renderer will send an IPC that a CacheID is deleted after each javascript cache object is deleted.
To address the change on the browser side, simply make a new CacheID for every call to GetCache and CreateCache and delete its corresponding refptr when the CacheID is dropped.
BUG=392621
Review URL: https://codereview.chromium.org/
599473002
Cr-Commit-Position: refs/heads/master@{#296390}