Desks: Prepare Virtual Desks Gestures for launch

This CL makes the following changes:
- Tab scrubbing will always use 3-finger gestures.
- 4-finger horizontal swipes will switch desks only if
  the flag "--enable-virtual-desks-gestures" is enabled.
- 3-finger horizontal swipes while in Overview will always
  move the highlighter.

This CL is meant to be merged back to M-79.
A follow-up CL will remove the "--enable-virtual-desks-gestures"
flag entirely on M-80, so that virtual desks gestures will always
be enabled going forward.

BUG=1005340
TEST=Tested manually on device, updated existing tests.

Change-Id: I1316e150556a4f2ede79b41dab8ddc3402d39370
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1902232
Commit-Queue: Ahmed Fakhry <afakhry@chromium.org>
Reviewed-by: James Cook <jamescook@chromium.org>
Cr-Commit-Position: refs/heads/master@{#713262}

ash/public/cpp/ash_features.h

@@ -98,8 +98,7 @@ ASH_PUBLIC_EXPORT extern const base::Feature kViewsLogin;
 // Enables the Virtual Desks feature.
 ASH_PUBLIC_EXPORT extern const base::Feature kVirtualDesks;
 
-// Enables the touchpad 3-finger gestures to switch desks. It also changes tab
-// scrubbing as well as overview highlight to use 4-finger gestures.
+// Enables the touchpad 4-finger gestures to switch desks.
 // This flag is only effective if the Virtual Desks feature is enabled (see
 // `kVirtualDesks`).
 ASH_PUBLIC_EXPORT extern const base::Feature kVirtualDesksGestures;

ash/wm/gestures/wm_gesture_handler.cc

@@ -47,7 +47,7 @@ bool Handle3FingerVerticalScroll(float scroll_y) {
   return true;
 }
 
-// Handles horizontal 3-finger scroll by switching desks if possible.
+// Handles horizontal 4-finger scroll by switching desks if possible.
 // Returns true if the gesture was handled.
 bool HandleDesksSwitchHorizontalScroll(float scroll_x) {
   DCHECK(CanHandleVirtualDesksGestures());
@@ -126,18 +126,17 @@ bool WmGestureHandler::EndScroll() {
     if (std::fabs(scroll_x) < std::fabs(scroll_y))
       return Handle3FingerVerticalScroll(scroll_y);
 
-    if (can_handle_desks_gestures_)
-      return HandleDesksSwitchHorizontalScroll(scroll_x);
+    return MoveOverviewSelection(finger_count, scroll_x, scroll_y);
   }
 
-  return MoveOverviewSelection(finger_count, scroll_x, scroll_y);
+  return finger_count == 4 && can_handle_desks_gestures_ &&
+         HandleDesksSwitchHorizontalScroll(scroll_x);
 }
 
 bool WmGestureHandler::MoveOverviewSelection(int finger_count,
                                              float scroll_x,
                                              float scroll_y) {
-  const int required_finger_count = can_handle_desks_gestures_ ? 4 : 3;
-  if (finger_count != required_finger_count)
+  if (finger_count != 3)
     return false;
 
   auto* overview_controller = Shell::Get()->overview_controller();

ash/wm/gestures/wm_gesture_handler_unittest.cc

@@ -23,6 +23,9 @@ namespace ash {
 
 namespace {
 
+constexpr int kNumFingersForHighlight = 3;
+constexpr int kNumFingersForDesksSwitch = 4;
+
 bool InOverviewSession() {
   return Shell::Get()->overview_controller()->InOverviewSession();
 }
@@ -32,10 +35,6 @@ bool CanHandleVirtualDesksGestures() {
          features::IsVirtualDesksGesturesEnabled();
 }
 
-int GetNumFingersForHighlight() {
-  return CanHandleVirtualDesksGestures() ? 4 : 3;
-}
-
 const aura::Window* GetHighlightedWindow() {
   return InOverviewSession() ? GetOverviewHighlightedWindow() : nullptr;
 }
@@ -72,7 +71,7 @@ class WmGestureHandlerTest : public AshTestBase,
     DeskSwitchAnimationWaiter waiter;
     const float x_offset =
         (scroll_left ? -1 : 1) * WmGestureHandler::kHorizontalThresholdDp;
-    Scroll(x_offset, 0, /*fingers=*/3);
+    Scroll(x_offset, 0, kNumFingersForDesksSwitch);
     waiter.Wait();
   }
 
@@ -123,7 +122,7 @@ TEST_P(WmGestureHandlerTest, HorizontalScrollInOverview) {
   auto scroll_until_window_highlighted = [this](float x_offset,
                                                 float y_offset) {
     do {
-      Scroll(x_offset, y_offset, GetNumFingersForHighlight());
+      Scroll(x_offset, y_offset, kNumFingersForHighlight);
     } while (!GetHighlightedWindow());
   };
 
@@ -154,10 +153,10 @@ TEST_P(WmGestureHandlerTest, HorizontalScrollInOverview) {
 // Tests that a mostly horizontal scroll does not trigger overview.
 TEST_P(WmGestureHandlerTest, HorizontalScrolls) {
   const float long_scroll = 2 * WmGestureHandler::kVerticalThresholdDp;
-  Scroll(long_scroll + 100, -long_scroll, GetNumFingersForHighlight());
+  Scroll(long_scroll + 100, -long_scroll, kNumFingersForHighlight);
   EXPECT_FALSE(InOverviewSession());
 
-  Scroll(-long_scroll - 100, -long_scroll, GetNumFingersForHighlight());
+  Scroll(-long_scroll - 100, -long_scroll, kNumFingersForHighlight);
   EXPECT_FALSE(InOverviewSession());
 }
 
@@ -209,7 +208,7 @@ TEST_P(DesksGestureHandlerTest, HorizontalScrolls) {
   // Tests that since there is no previous desk, we remain on the same desk when
   // scrolling right.
   const float long_scroll = WmGestureHandler::kHorizontalThresholdDp;
-  Scroll(long_scroll, 0.f, 3);
+  Scroll(long_scroll, 0.f, kNumFingersForDesksSwitch);
   EXPECT_EQ(desk_controller->desks()[0].get(), desk_controller->active_desk());
 }
 
@@ -224,16 +223,17 @@ TEST_P(DesksGestureHandlerTest, NoDeskChanges) {
   const float short_scroll = WmGestureHandler::kHorizontalThresholdDp - 10.f;
   const float long_scroll = WmGestureHandler::kHorizontalThresholdDp;
   // Tests that a short horizontal scroll does not switch desks.
-  Scroll(short_scroll, 0.f, 3);
+  Scroll(short_scroll, 0.f, kNumFingersForDesksSwitch);
   EXPECT_EQ(desk_controller->desks()[0].get(), desk_controller->active_desk());
 
   // Tests that a scroll that meets the horizontal requirements, but is mostly
   // vertical does not switch desks.
-  Scroll(long_scroll, long_scroll + 10.f, 3);
+  Scroll(long_scroll, long_scroll + 10.f, kNumFingersForDesksSwitch);
   EXPECT_EQ(desk_controller->desks()[0].get(), desk_controller->active_desk());
 
   // Tests that a vertical scroll does not switch desks.
-  Scroll(0.f, WmGestureHandler::kVerticalThresholdDp, 3);
+  Scroll(0.f, WmGestureHandler::kVerticalThresholdDp,
+         kNumFingersForDesksSwitch);
   EXPECT_EQ(desk_controller->desks()[0].get(), desk_controller->active_desk());
 }
 
@@ -248,7 +248,7 @@ TEST_P(DesksGestureHandlerTest, NoDoubleDeskChange) {
 
   const float long_scroll = WmGestureHandler::kHorizontalThresholdDp * 3;
   DeskSwitchAnimationWaiter waiter;
-  Scroll(-long_scroll, 0, 3);
+  Scroll(-long_scroll, 0, kNumFingersForDesksSwitch);
   waiter.Wait();
   EXPECT_EQ(desk_controller->desks()[1].get(), desk_controller->active_desk());
 }

chrome/browser/ui/ash/tab_scrubber.cc

@@ -8,7 +8,6 @@
 
 #include <algorithm>
 
-#include "ash/public/cpp/ash_features.h"
 #include "ash/shell.h"
 #include "base/bind.h"
 #include "base/metrics/histogram_macros.h"
@@ -26,17 +25,6 @@
 #include "ui/events/event_utils.h"
 #include "ui/events/gesture_detection/gesture_configuration.h"
 
-namespace {
-
-int GetRequiredNumberOfFingers() {
-  return ash::features::IsVirtualDesksEnabled() &&
-                 ash::features::IsVirtualDesksGesturesEnabled()
-             ? 4
-             : 3;
-}
-
-}  // namespace
-
 // static
 TabScrubber* TabScrubber::GetInstance() {
   static TabScrubber* instance = nullptr;
@@ -79,8 +67,7 @@ bool TabScrubber::IsActivationPending() {
   return activate_timer_.IsRunning();
 }
 
-TabScrubber::TabScrubber()
-    : required_finger_count_(GetRequiredNumberOfFingers()) {
+TabScrubber::TabScrubber() {
   // TODO(mash): Add window server API to observe swipe gestures. Observing
   // gestures on browser windows is not sufficient, as this feature works when
   // the cursor is over the shelf, desktop, etc. https://crbug.com/796366
@@ -100,7 +87,7 @@ void TabScrubber::OnScrollEvent(ui::ScrollEvent* event) {
     return;
   }
 
-  if (event->finger_count() != required_finger_count_)
+  if (event->finger_count() != 3)
     return;
 
   Browser* browser = GetActiveBrowser();

chrome/browser/ui/ash/tab_scrubber.h

@@ -76,9 +76,6 @@ class TabScrubber : public ui::EventHandler,
 
   void UpdateHighlightedTab(Tab* new_tab, int new_index);
 
-  // The required number of fingers to perform tab scrubbing, which can be
-  // affected by some Virtual Desks flags.
-  const int required_finger_count_;
   // Are we currently scrubbing?.
   bool scrubbing_ = false;
   // The last browser we used for scrubbing, NULL if |scrubbing_| is false and