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We are in the midst of componentizing ExternalNavigationHandler.java for
reuse by WebLayer. The main remaining //chrome-level dependency is on
TabRedirectHandler.java. Unlike other dependencies, this dependency can
neither be easily componentized (it is essentially //chrome-level
functionality) nor can it be easily abstracted through
ExternalNavigationDelegate.java. The reason for the latter is that
the TabRedirectHandler instance is necessarily accessed through the
ExternalNavigationParams instance as it is tied to the navigation in
question, and if we were to remove all knowledge of it from
ExternalNavigationParams, there would be no straightforward way to
plumb it into //chrome's ExternalNavigationDelegateImpl.

This CL instead creates a RedirectHandler interface that contains the
methods needed by ExternalNavigationHandler. ExternalNavigationParams
and ExternalNavigationHandler are changed to talk in terms of this
interface, which TabRedirectHandler implements. This approach has the
additional benefit that it leaves existing logic coalesced within
ExternalNavigationHandler, which will make it easier to adapt this
logic in the WebLayer context as needed.

For this initial delegate interface, we have preserved the shape of the
interface to be the exact current usage by
ExternalNavigationHandler.java. Future work can refine the interface to
have it be as thin and logical as possible, potentially coalescing some
low-level methods into a smaller number of higher-level ones.

Bug: 1031465
Change-Id: I5b9568f371c248e8fd2d52429725ed0a44a098a2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2095719
Commit-Queue: Colin Blundell <blundell@chromium.org>
Reviewed-by: Michael Thiessen <mthiesse@chromium.org>
Cr-Commit-Position: refs/heads/master@{#748747}