Revert "Activate the next/previous tab on horizonal scroll"

This effectively reverts commit 90496b3b.

This turns out to be unpopular, as well as causing issues on the Mac,
particularly with Magic Mice.

BUG=2384,965753

Change-Id: I69803bcbde01b1978c58ef1454280ac08403a24d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1730631Reviewed-by: Peter Boström <pbos@chromium.org>
Commit-Queue: Avi Drissman <avi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#683311}

chrome/browser/ui/views/tabs/tab_strip.cc

@@ -1871,34 +1871,6 @@ void TabStrip::Layout() {
   CompleteAnimationAndLayout();
 }
 
-bool TabStrip::OnMouseWheel(const ui::MouseWheelEvent& event) {
-  // Change the selected tab on horizontal wheel scrolls.
-  // Honor wheel scrolls over the tabs themselves, but not the NTB/surrounding
-  // space.
-  if ((!event.x_offset() && !event.IsShiftDown()) || tab_count() < 2 ||
-      !FindTabHitByPoint(event.location()))
-    return false;
-
-  accumulated_horizontal_scroll_ +=
-      (event.x_offset() ? event.x_offset() : event.y_offset());
-
-  int horizontal_offset =
-      accumulated_horizontal_scroll_ / ui::MouseWheelEvent::kWheelDelta;
-  if (!horizontal_offset)
-    return true;
-
-  accumulated_horizontal_scroll_ %= ui::MouseWheelEvent::kWheelDelta;
-
-  int new_active_index =
-      (controller_->GetActiveIndex() + horizontal_offset) % tab_count();
-  if (new_active_index < 0)
-    new_active_index += tab_count();
-
-  DCHECK(IsValidModelIndex(new_active_index));
-  controller_->SelectTab(new_active_index, event);
-  return true;
-}
-
 void TabStrip::PaintChildren(const views::PaintInfo& paint_info) {
   // This is used to log to UMA. NO EARLY RETURNS!
   base::ElapsedTimer paint_timer;

chrome/browser/ui/views/tabs/tab_strip.h

@@ -282,7 +282,6 @@ class TabStrip : public views::AccessiblePaneView,
 
   // views::AccessiblePaneView:
   void Layout() override;
-  bool OnMouseWheel(const ui::MouseWheelEvent& event) override;
   void PaintChildren(const views::PaintInfo& paint_info) override;
   const char* GetClassName() const override;
   gfx::Size CalculatePreferredSize() const override;
@@ -640,10 +639,6 @@ class TabStrip : public views::AccessiblePaneView,
   // Number of mouse moves.
   int mouse_move_count_ = 0;
 
-  // Accumulatated offsets from thumb wheel. Used to throttle horizontal
-  // scroll from thumb wheel.
-  int accumulated_horizontal_scroll_ = 0;
-
   // Timer used when a tab is closed and we need to relayout. Only used when a
   // tab close comes from a touch device.
   base::OneShotTimer resize_layout_timer_;

chrome/browser/ui/views/tabs/tab_strip_unittest.cc

@@ -975,52 +975,6 @@ TEST_P(TabStripTest, EventsOnClosingTab) {
   EXPECT_EQ(first_tab, tab_strip_->GetEventHandlerForPoint(tab_center));
 }
 
-// Switch selected tabs on horizontal scroll events.
-TEST_P(TabStripTest, HorizontalScroll) {
-  tab_strip_->SetBounds(0, 0, 200, 20);
-
-  for (int i = 0; i < 3; i++)
-    controller_->AddTab(i, true /* is_active */);
-
-  Tab* tab = tab_strip_->tab_at(0);
-  gfx::Point tab_center = tab->bounds().CenterPoint();
-
-  for (int i = 0; i < tab_strip_->tab_count(); ++i) {
-    ui::MouseWheelEvent wheel_event(
-        gfx::Vector2d(ui::MouseWheelEvent::kWheelDelta, 0), tab_center,
-        tab_center, ui::EventTimeForNow(), 0, 0);
-    tab_strip_->OnMouseWheel(wheel_event);
-    EXPECT_EQ(i, controller_->GetActiveIndex());
-  }
-
-  controller_->SelectTab(0, dummy_event_);
-  for (int i = tab_strip_->tab_count() - 1; i >= 0; --i) {
-    ui::MouseWheelEvent wheel_event(
-        gfx::Vector2d(-ui::MouseWheelEvent::kWheelDelta, 0), tab_center,
-        tab_center, ui::EventTimeForNow(), 0, 0);
-    tab_strip_->OnMouseWheel(wheel_event);
-    EXPECT_EQ(i, controller_->GetActiveIndex());
-  }
-
-  // When offset is smaller than kWheelDelta, we don't scroll immediately.
-  // We wait offset until accumulated offset gets bigger than kWheelDelta.
-  const int small_offset = ui::MouseWheelEvent::kWheelDelta / 3;
-  int next_accumulated_offset = small_offset;
-  while (next_accumulated_offset < ui::MouseWheelEvent::kWheelDelta) {
-    ui::MouseWheelEvent wheel_event(gfx::Vector2d(small_offset, 0), tab_center,
-                                    tab_center, ui::EventTimeForNow(), 0, 0);
-    tab_strip_->OnMouseWheel(wheel_event);
-
-    EXPECT_EQ(0, controller_->GetActiveIndex());
-    next_accumulated_offset += small_offset;
-  }
-
-  ui::MouseWheelEvent wheel_event(gfx::Vector2d(small_offset, 0), tab_center,
-                                  tab_center, ui::EventTimeForNow(), 0, 0);
-  tab_strip_->OnMouseWheel(wheel_event);
-  EXPECT_EQ(1, controller_->GetActiveIndex());
-}
-
 TEST_P(TabStripTest, AnimationOnTabAdd) {
   tab_strip_->SetBounds(0, 0, 1000, 100);
   // Show widget to enable animations.