[ash-md] Adds support for gesture to move selection in overview mode

ash/wm/gestures/overview_gesture_handler.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ash/wm/gestures/overview_gesture_handler.h"
 
 #include "ash/common/wm/overview/window_selector_controller.h"
 #include "ash/common/wm_shell.h"
 #include "ui/events/event.h"
 #include "ui/events/event_constants.h"
 
 namespace ash {
-namespace {
 
-// The threshold before engaging overview on a three finger swipe on the
-// touchpad.
-const float kSwipeThresholdPixels = 300;
+// The threshold before engaging overview with a touchpad three-finger scroll.
+const float OverviewGestureHandler::vertical_threshold_pixels_ = 300;
 
-}  // namespace
+// The threshold before moving selector horizontally when using a touchpad
+// three-finger scroll.
+const float OverviewGestureHandler::horizontal_threshold_pixels_ = 330;
 
 OverviewGestureHandler::OverviewGestureHandler() : scroll_x_(0), scroll_y_(0) {}
 
 OverviewGestureHandler::~OverviewGestureHandler() {}
 
 bool OverviewGestureHandler::ProcessScrollEvent(const ui::ScrollEvent& event) {
   if (event.type() == ui::ET_SCROLL_FLING_START ||
       event.type() == ui::ET_SCROLL_FLING_CANCEL || event.finger_count() != 3) {
     scroll_x_ = scroll_y_ = 0;
     return false;
   }
 
   scroll_x_ += event.x_offset();
   scroll_y_ += event.y_offset();
 
-  // Horizontal swiping is ignored.
+  WindowSelectorController* window_selector_controller =
+      WmShell::Get()->window_selector_controller();
+
+  // Horizontal 3-finger scroll moves selection when already in overview mode.
   if (std::fabs(scroll_x_) >= std::fabs(scroll_y_)) {
+    if (!window_selector_controller->IsSelecting()) {
+      scroll_x_ = scroll_y_ = 0;
+      return false;
+    }
+    if (std::fabs(scroll_x_) < horizontal_threshold_pixels_)
+      return false;
+
+    const int increment = scroll_x_ > 0 ? 1 : -1;
     scroll_x_ = scroll_y_ = 0;
-    return false;
+    window_selector_controller->IncrementSelection(increment);
+    return true;
   }
 
-  // Only allow swipe up to enter overview, down to exit. Ignore extra swiping
-  // in the wrong direction.
-  WindowSelectorController* window_selector_controller =
-      WmShell::Get()->window_selector_controller();
+  // Use vertical 3-finger scroll gesture up to enter overview, down to exit.
   if (window_selector_controller->IsSelecting()) {
     if (scroll_y_ < 0)
       scroll_x_ = scroll_y_ = 0;
-    if (scroll_y_ < kSwipeThresholdPixels)
+    if (scroll_y_ < vertical_threshold_pixels_)
       return false;
   } else {
     if (scroll_y_ > 0)
       scroll_x_ = scroll_y_ = 0;
-    if (scroll_y_ > -kSwipeThresholdPixels)
+    if (scroll_y_ > -vertical_threshold_pixels_)
       return false;
   }
 
   // Reset scroll amount on toggling.
   scroll_x_ = scroll_y_ = 0;
   WmShell::Get()->RecordUserMetricsAction(UMA_TOUCHPAD_GESTURE_OVERVIEW);
+  if (window_selector_controller->IsSelecting() &&
+      window_selector_controller->AcceptSelection()) {
+    return true;
+  }
   window_selector_controller->ToggleOverview();
   return true;
 }
 
 }  // namespace ash