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This CL mainly adds the download later dialog UI xml file and the string
resources.

The view logic is not implemented. A very basic instrumentation test is
added to test the download later dialog Java code.

A Jni bridge will eventually own DownloadLaterDialogCoordinator.

Bug: 1078454
Change-Id: I3508415e437371b38facd7c9ce78b3276f7fa7e3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2223001
Commit-Queue: Xing Liu <xingliu@chromium.org>
Reviewed-by: Shakti Sahu <shaktisahu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#774824}