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Add a whitelisting manager for safebrowsing. This code will be plumbed
to an Android WebView API so that applications can whitelist 
(i.e. prevent) domains from being checked by Safebrowsing logic.
 
The main rules are:
- if host has a leading ".", it needs to be exact to be whitelisted.
- if host does not have a leading ".", subdomains are also whitelisted.

Invalid schemes are also ignored. Note that Safebrowsing only works on h
ttp/https and in future ws urls.

Bug: 726770
Change-Id: Icbffebd87472286508f1902cd6323ce58faee797
Reviewed-on: https://chromium-review.googlesource.com/563520
Commit-Queue: Selim Gurun <sgurun@chromium.org>
Reviewed-by: Varun Khaneja <vakh@chromium.org>
Reviewed-by: Eric Roman <eroman@chromium.org>
Reviewed-by: Nate Fischer <ntfschr@chromium.org>
Reviewed-by: Bo Liu <boliu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#487567}