back_gesture: Get x drag amount from touch events.

scroll_x() of gesture event is not reliable after checked on physical
device. Get the x drag amount from touch events as y drag amount.

Fling event is supported, which means the |drag_progress_| might
hasn't reached full progress while COMPLETING the drag.

Bug: 1002733
Change-Id: I66dfb4110e2e8f34445d67a5e5cc25681b3f8708
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1879821
Commit-Queue: Min Chen <minch@chromium.org>
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#709295}

ash/wm/back_gesture_affordance.cc

@@ -232,8 +232,6 @@ void BackGestureAffordance::Abort() {
 
 void BackGestureAffordance::Complete() {
   DCHECK_EQ(State::DRAGGING, state_);
-  DCHECK_LE(1.f, drag_progress_);
-
   state_ = State::COMPLETING;
 
   animation_ = std::make_unique<gfx::LinearAnimation>(

ash/wm/toplevel_window_event_handler.cc

@@ -539,10 +539,12 @@ void ToplevelWindowEventHandler::OnTouchEvent(ui::TouchEvent* event) {
   if (event->type() == ui::ET_TOUCH_RELEASED)
     first_touch_id_ = ui::kPointerIdUnknown;
 
-  if (event->type() == ui::ET_TOUCH_PRESSED)
-    y_drag_amount_ = 0;
-  else
+  if (event->type() == ui::ET_TOUCH_PRESSED) {
+    x_drag_amount_ = y_drag_amount_ = 0;
+  } else {
+    x_drag_amount_ += (event->location().x() - last_touch_point_.x());
     y_drag_amount_ += (event->location().y() - last_touch_point_.y());
+  }
 
   last_touch_point_ = event->location();
 }
@@ -909,7 +911,6 @@ bool ToplevelWindowEventHandler::HandleGoingBackFromLeftEdge(
       going_back_started_ = StartedAwayFromLeftArea(event);
       if (!going_back_started_)
         break;
-      x_drag_amount_ = 0;
       back_gesture_affordance_ =
           std::make_unique<BackGestureAffordance>(screen_location);
       return true;
@@ -918,7 +919,6 @@ bool ToplevelWindowEventHandler::HandleGoingBackFromLeftEdge(
       if (!going_back_started_)
         break;
       DCHECK(back_gesture_affordance_);
-      x_drag_amount_ += event->details().scroll_x();
       back_gesture_affordance_->SetDragProgress(x_drag_amount_, y_drag_amount_);
       return true;
     case ui::ET_GESTURE_SCROLL_END:
@@ -927,7 +927,7 @@ bool ToplevelWindowEventHandler::HandleGoingBackFromLeftEdge(
         break;
       DCHECK(back_gesture_affordance_);
       if ((event->type() == ui::ET_GESTURE_SCROLL_END &&
-           screen_location.x() >= kSwipingDistanceForGoingBack) ||
+           x_drag_amount_ >= kSwipingDistanceForGoingBack) ||
           (event->type() == ui::ET_SCROLL_FLING_START &&
            event->details().velocity_x() >= kFlingVelocityForGoingBack)) {
         aura::Window* root_window =

ash/wm/toplevel_window_event_handler.h

@@ -193,17 +193,12 @@ class ASH_EXPORT ToplevelWindowEventHandler
   // True if swiping from left edge to go to previous page is in progress.
   bool going_back_started_ = false;
 
-  // Tracks the y-axis drag amount through touch events. Used for back gesture
-  // affordance in tablet mode. The gesture movement of back gesture can't be
-  // recognized by GestureRecognizer, which leads to wrong gesture locations of
-  // back gesture. See crbug.com/1015464 for the details.
-  int y_drag_amount_ = 0;
-
-  // Tracks the x-axis drag amount through gesture events. Used for back gesture
-  // affordance in tablet mode. Note, gets the drag amount from gesture events
-  // instead of touch events, since the x location of the gestures is reliable
-  // during back gesture movements.
+  // Tracks the x-axis and y-axis drag amount through touch events. Used for
+  // back gesture affordance in tablet mode. The gesture movement of back
+  // gesture can't be recognized by GestureRecognizer, which leads to wrong
+  // gesture locations of back gesture. See crbug.com/1015464 for the details.
   int x_drag_amount_ = 0;
+  int y_drag_amount_ = 0;
 
   // Position of last touch event. Used to calculate |y_drag_amount_|. Note,
   // only touch events from |first_touch_id_| will be recorded.