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This is a part of implementation of class Uri. This CL contains
implementation of getters along with algorithm to encode disallowed
characters with % sign.
Other CLs:
 - https://crrev.com/c/2103143
 - https://crrev.com/c/2123640

BUG=chromium:821497
TEST=on my workstation

Change-Id: Iabe72b7d9907743345a886fe3ffb2dc19b1b76b2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2118426
Commit-Queue: Piotr Pawliczek <pawliczek@chromium.org>
Reviewed-by: Sean Kau <skau@chromium.org>
Cr-Commit-Position: refs/heads/master@{#758049}