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This will enable tests to receive callback executions from FakeWebFrame
and configure what FakeWebFrame passes to callback. Also allows for
configuring CanCallJavascriptFunction to return false.

Change-Id: I5b84d88c2df0e30ec7d81b48b0cf9a5c66a18c51
Reviewed-on: https://chromium-review.googlesource.com/c/1482136
Commit-Queue: Chris Lu <thegreenfrog@chromium.org>
Reviewed-by: Eugene But <eugenebut@chromium.org>
Cr-Commit-Position: refs/heads/master@{#636083}