ozone/wayland: Fix horizontal scroll direction

wl_pointer's horizontal offsets were being handled differently from
vertical ones. This causes the effect observed in crbug.com/986258.
This CL fixes it as well as updates the associated test expectations.

Test: Covered by ozone_unitests. Also, testable manually as follows:
  - Open any webpage with horizontal scroll bar;
  - Scroll it, using either a touchpad or mouse;
  - In Sway compositor, the following command can be used to enable
    "natural scroll", as mentioned in the bug report:
    $ swaymsg input "<touchpad id here>" natural_scroll enabled
  - whereas touchpad id is retrieved through 'swaymsg -t get_inputs'
  command.

R=msisov@igalia.com

Bug: 986258
Change-Id: I0bb835aae47ff0bcb99b67b39d32738b0088a80e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2579652Reviewed-by: Antonio Gomes <tonikitoo@igalia.com>
Commit-Queue: Nick Yamane <nickdiego@igalia.com>
Cr-Commit-Position: refs/heads/master@{#835392}

ui/ozone/platform/wayland/host/wayland_pointer.cc

@@ -130,7 +130,7 @@ void WaylandPointer::Axis(void* data,
     offset.set_y(-wl_fixed_to_double(value) / kAxisValueScale *
                  MouseWheelEvent::kWheelDelta);
   } else if (axis == WL_POINTER_AXIS_HORIZONTAL_SCROLL) {
-    offset.set_x(wl_fixed_to_double(value) / kAxisValueScale *
+    offset.set_x(-wl_fixed_to_double(value) / kAxisValueScale *
                  MouseWheelEvent::kWheelDelta);
   } else {
     return;

ui/ozone/platform/wayland/host/wayland_pointer_unittest.cc

@@ -234,7 +234,7 @@ TEST_P(WaylandPointerTest, AxisHorizontal) {
   ASSERT_TRUE(event);
   ASSERT_TRUE(event->IsMouseWheelEvent());
   auto* mouse_wheel_event = event->AsMouseWheelEvent();
-  EXPECT_EQ(gfx::Vector2d(MouseWheelEvent::kWheelDelta, 0),
+  EXPECT_EQ(gfx::Vector2d(-MouseWheelEvent::kWheelDelta, 0),
             mouse_wheel_event->offset());
   EXPECT_EQ(EF_LEFT_MOUSE_BUTTON, mouse_wheel_event->button_flags());
   EXPECT_EQ(0, mouse_wheel_event->changed_button_flags());
@@ -340,11 +340,11 @@ TEST_P(WaylandPointerTest, FlingVertical) {
   EXPECT_EQ(ET_SCROLL_FLING_START, scroll_event->type());
   EXPECT_EQ(gfx::PointF(50, 75), scroll_event->location_f());
   EXPECT_EQ(0.0f, scroll_event->x_offset());
+  EXPECT_EQ(0.0f, scroll_event->x_offset_ordinal());
   // Initial vertical velocity depends on the implementation outside of
   // WaylandPointer, but it should be negative value based on the direction of
   // recent two axis events.
   EXPECT_GT(0.0f, scroll_event->y_offset());
-  EXPECT_EQ(0.0f, scroll_event->x_offset_ordinal());
   EXPECT_GT(0.0f, scroll_event->y_offset_ordinal());
 }
 
@@ -393,13 +393,13 @@ TEST_P(WaylandPointerTest, FlingHorizontal) {
   auto* scroll_event = event3->AsScrollEvent();
   EXPECT_EQ(ET_SCROLL_FLING_START, scroll_event->type());
   EXPECT_EQ(gfx::PointF(50, 75), scroll_event->location_f());
-  // Initial horizontal velocity depends on the implementation outside of
-  // WaylandPointer, but it should be positive value based on the direction of
-  // recent two axis events.
-  EXPECT_LT(0.0f, scroll_event->x_offset());
   EXPECT_EQ(0.0f, scroll_event->y_offset());
-  EXPECT_LT(0.0f, scroll_event->x_offset_ordinal());
   EXPECT_EQ(0.0f, scroll_event->y_offset_ordinal());
+  // Initial horizontal velocity depends on the implementation outside of
+  // WaylandPointer, but it should be negative value based on the direction of
+  // recent two axis events.
+  EXPECT_GT(0.0f, scroll_event->x_offset());
+  EXPECT_GT(0.0f, scroll_event->x_offset_ordinal());
 }
 
 TEST_P(WaylandPointerTest, FlingCancel) {
@@ -518,10 +518,10 @@ TEST_P(WaylandPointerTest, FlingDiagonal) {
   auto* scroll_event = event5->AsScrollEvent();
   EXPECT_EQ(ET_SCROLL_FLING_START, scroll_event->type());
   EXPECT_EQ(gfx::PointF(50, 75), scroll_event->location_f());
-  // Check the offset direction. It should non-zero in both directions.
-  EXPECT_LT(0.0f, scroll_event->x_offset());
+  // Check the offset direction. It should non-zero in both axes.
+  EXPECT_GT(0.0f, scroll_event->x_offset());
   EXPECT_GT(0.0f, scroll_event->y_offset());
-  EXPECT_LT(0.0f, scroll_event->x_offset_ordinal());
+  EXPECT_GT(0.0f, scroll_event->x_offset_ordinal());
   EXPECT_GT(0.0f, scroll_event->y_offset_ordinal());
   // Horizontal offset should be larger than vertical one, given the scroll
   // offset in each direction.