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This CL is a precursor to moving ThinWebView to components. Only
dependency on chrome layer was TabHelpers which was moved to a
ThinWebViewInitializer interface.

Bug: 1116770
Change-Id: I24fdd93e35ae24d9bede953e32c68b0fd7024ada
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2358993
Commit-Queue: Shakti Sahu <shaktisahu@chromium.org>
Reviewed-by: David Trainor <dtrainor@chromium.org>
Cr-Commit-Position: refs/heads/master@{#799355}