testTriggeringContextualSearchHidesFindInPageOverlay is flaky, and super-flaky on Nougat.

testSecondTapWithSmartSelection is flaky (issue 778693)

Some possible reasons for flakiness:
A) We use pollInstrumentationThread instead of pollUiThread (the latter is recommended by CriteriaHelper).
B) We don't check that simulated taps are actually recognized (though the underlying function returns a success boolean).
C) Issue 778540 where cancelling animation (fix pending).  I saw some tests get stuck waiting for the panel to peek but it was already peeked.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/42fb77482d7b6d3b3c19a5c09a56416a42c71764

commit 42fb77482d7b6d3b3c19a5c09a56416a42c71764
Author: Donn Denman <donnd@google.com>
Date: Mon Oct 30 19:37:53 2017

[TTS] Fix flaky test hiding the FindInPageOverlay.

The testTriggeringContextualSearchHidesFindInPageOverlay has been
very flaky recently, and it looks like the problem is due to clicks
in the content not triggering Contextual Search.  There's probably
a race condition between scrolling to put the word to click into
view and scrolling for the Find target.  The fix is to not type
any Find target to avoid the scroll.

BUG=765462

Change-Id: I007f7fa986e2528d7b7f9a4829be08c566572433
Reviewed-on: https://chromium-review.googlesource.com/742147
Reviewed-by: Theresa <twellington@chromium.org>
Commit-Queue: Donn Denman <donnd@chromium.org>
Cr-Commit-Position: refs/heads/master@{#512581}
[modify] https://crrev.com/42fb77482d7b6d3b3c19a5c09a56416a42c71764/chrome/android/javatests/src/org/chromium/chrome/browser/contextualsearch/ContextualSearchManagerTest.java

We should do a general update on various tests for CS including flakes.