[Chromeshine] Create PageViewObserver for CCT at task root

We usually don't want to observe custom tab browsing, since it should be
attributed to the app that opens the custom tab. The exception is when
the custom tab is at the root of the task, e.g. when links are opened
from the "-1 screen."

(cherry picked from commit 067a6581ae468209436c38d5bccb266519aa5013)

Bug: 973232
Change-Id: I22b5cad63d56f60cf43adbadfcdd03ba8e964212
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1652666
Reviewed-by: Peter Conn <peconn@chromium.org>
Commit-Queue: Patrick Noland <pnoland@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#669304}
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1662850
Reviewed-by: Patrick Noland <pnoland@chromium.org>
Cr-Commit-Position: refs/branch-heads/3809@{#377}
Cr-Branched-From: d82dec1a818f378c464ba307ddd9c92133eac355-refs/heads/master@{#665002}

• chrome/android/java/src/org/chromium/chrome/browser/customtabs/CustomTabActivity.java[diff]