[Android] Suppress pull-to-refresh when overscroll glow visible

Avoid accidental refreshes by suppressing the effect when the overscroll
glow animation is still visible. This naturally prevents the case where
the user repeatedly flings/scrolls to the top, releasing before they
realize that the scroll has turned into a pull-to-refresh.

Note that suppression is only provided on L; the glow effect on previous
platforms is both too long and too visually faint to provide a good feedback
signal for when the user can start pulling to refresh.

BUG=456300

Review URL: https://codereview.chromium.org/879273007

Cr-Commit-Position: refs/heads/master@{#315832}
(cherry picked from commit 2dbb7e87a8cd907e4d782cff5212dc6f61626e7d)

Review URL: https://codereview.chromium.org/935833003

Cr-Commit-Position: refs/branch-heads/2272@{#319}
Cr-Branched-From: 827a380cfdb31aa54c8d56e63ce2c3fd8c3ba4d4-refs/heads/master@{#310958}

• content/browser/android/overscroll_controller_android.cc[diff]
• content/browser/android/overscroll_glow.cc[diff]
• content/browser/android/overscroll_glow.h[diff]
• content/browser/android/overscroll_refresh.cc[diff]
• content/browser/android/overscroll_refresh.h[diff]
• content/browser/android/overscroll_refresh_unittest.cc[diff]