GitLab

Implement live page sharing:
- Adding a new temporary client namespace for the usage of live page
  sharing, which has a limit of one page per url and expiration period
  as one hour.
- Adding saveAndSharePage in OfflinePageUtils, implementing the workflow
  of save page, get page and share page.

Bug: 870895
Change-Id: Iab5f074dfa955ba30f8b125a70cedb87e8610246
Reviewed-on: https://chromium-review.googlesource.com/1162827Reviewed-by: Peter Williamson <petewil@chromium.org>
Reviewed-by: Theresa <twellington@chromium.org>
Commit-Queue: Yafei Duan <romax@chromium.org>
Cr-Commit-Position: refs/heads/master@{#582418}