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This implements basic client hints functionality. Still TODO after this
patch to make sure ContentSettingsAgentImpl is working as expected:
- Sync content settings to renderer
- Add ContentSettingsManager implementation for WebLayer

Bug: 1065537
Change-Id: I3a281c2a6a472ba9e1d79ff860d5bb94367cf888
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2145156
Commit-Queue: Clark DuVall <cduvall@chromium.org>
Reviewed-by: John Abd-El-Malek <jam@chromium.org>
Cr-Commit-Position: refs/heads/master@{#759401}