[chromecast] Clean up gesture state between side swipes.

  - Prevent crashes caused by incomplete gesture state when side swipes
    occur while using side swipe gestures between multiple views.

Bug: internal b/111100155
Test: manual
Change-Id: I5bd91b9322afc06e2ee69b5f311d60c8e373a5ed
Reviewed-on: https://chromium-review.googlesource.com/1155378Reviewed-by: Alex Sakhartchouk <alexst@chromium.org>
Commit-Queue: Ryan Daum <rdaum@chromium.org>
Cr-Commit-Position: refs/heads/master@{#579122}

chromecast/graphics/cast_system_gesture_event_handler.cc

@@ -184,11 +184,14 @@ ui::EventRewriteStatus SideSwipeDetector::RewriteEvent(
     VLOG(1) << "side swipe gesture begin @ " << touch_location.ToString();
     current_swipe_time_ = base::ElapsedTimer();
 
-
     // Stash a copy of the event should we decide to reconstitute it later if we
     // decide that this isn't in fact a side swipe.
     StashEvent(*touch_event);
 
+    // Avoid corrupt gesture state caused by a missing kGestureScrollEnd event
+    // as we potentially transition between web views.
+    root_window_->CleanupGestureState();
+
     // And then stop the original event from propagating.
     return ui::EVENT_REWRITE_DISCARD;
   }