Autoclick can start gesture timer when mouse leaves scroll button.

This fixes a bug where users feel like it's hard to hit the close
button within the scroll pad.

Bug: 984669
Change-Id: I6f241afc011a1e713e74c87f00dba364fe895fd8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1715549
Auto-Submit: Katie Dektar <katie@chromium.org>
Commit-Queue: Anastasia Helfinstein <anastasi@google.com>
Reviewed-by: Anastasia Helfinstein <anastasi@google.com>
Cr-Commit-Position: refs/heads/master@{#680476}

ash/autoclick/autoclick_controller.cc

@@ -261,6 +261,9 @@ void AutoclickController::OnEnteredScrollButton() {
 
 void AutoclickController::OnExitedScrollButton() {
   over_scroll_button_ = false;
+  // Reset the anchor_location_ so that gestures could begin immediately.
+  anchor_location_ = gfx::Point(-kDefaultAutoclickMovementThreshold,
+                                -kDefaultAutoclickMovementThreshold);
 }
 
 void AutoclickController::OnAutoclickScrollableBoundsFound(