split view: Change initial value of divider_closest_ratio_ from 0 to NaN

Before the present CL, SplitViewController::OnDisplayMetricsChanged
checks divider_closest_ratio_ against its initial value zero, which is
actually a "legitimate" value (it represents the divider position at the
extreme left or top). The present CL changes that initial value to NaN.

Test: ash_unittests SplitViewControllerTest.InternalDisplayConfigurationChangeDuringDividerSnapToLeft
Bug: 1006859
Change-Id: I1a89ea4b75d599251d77297449fd1d3a253eca26
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1815916Reviewed-by: Xiaoqian Dai <xdai@chromium.org>
Commit-Queue: Avery Musbach <amusbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#699546}

ash/wm/splitview/split_view_controller.cc

@@ -703,7 +703,7 @@ void SplitViewController::EndSplitView(EndReason end_reason) {
   black_scrim_layer_.reset();
   default_snap_position_ = NONE;
   divider_position_ = -1;
-  divider_closest_ratio_ = 0.f;
+  divider_closest_ratio_ = std::numeric_limits<float>::quiet_NaN();
   snapping_window_transformed_bounds_map_.clear();
 
   UpdateSplitViewStateAndNotifyObservers();
@@ -1111,7 +1111,7 @@ void SplitViewController::OnDisplayMetricsChanged(
     const int divider_thickness =
         std::min(divider_size.width(), divider_size.height());
     // Set default |divider_closest_ratio_| to kFixedPositionRatios[1].
-    if (!divider_closest_ratio_)
+    if (std::isnan(divider_closest_ratio_))
       divider_closest_ratio_ = kFixedPositionRatios[1];
 
     // Reverse the position ratio if top/left window changes.

ash/wm/splitview/split_view_controller.h

@@ -5,6 +5,7 @@
 #ifndef ASH_WM_SPLITSVIEW_SPLIT_VIEW_CONTROLLER_H_
 #define ASH_WM_SPLITSVIEW_SPLIT_VIEW_CONTROLLER_H_
 
+#include <limits>
 #include <memory>
 
 #include "ash/accessibility/accessibility_observer.h"
@@ -426,7 +427,7 @@ class ASH_EXPORT SplitViewController : public SplitViewNotifier,
   // kOneThirdPositionRatio and kTwoThirdPositionRatio based on current
   // |divider_position_|. Used to update |divider_position_| on work area
   // changes.
-  float divider_closest_ratio_ = 0.f;
+  float divider_closest_ratio_ = std::numeric_limits<float>::quiet_NaN();
 
   // The location of the previous mouse/gesture event in screen coordinates.
   gfx::Point previous_event_location_;

ash/wm/splitview/split_view_controller_unittest.cc

@@ -863,10 +863,58 @@ TEST_F(SplitViewControllerTest,
 }
 
 // Test that if the internal screen display configuration changes during the
-// divider snap animation, and if the adjusted divider bounds place it at an
-// edge of the screen, then split view ends.
+// divider snap animation, and if the adjusted divider bounds place it at the
+// left edge of the screen, then split view ends.
 TEST_F(SplitViewControllerTest,
-       InternalDisplayConfigurationChangeDuringDividerSnapToEndSplitView) {
+       InternalDisplayConfigurationChangeDuringDividerSnapToLeft) {
+  UpdateDisplay("407x400");
+  int64_t display_id = display::Screen::GetScreen()->GetPrimaryDisplay().id();
+  display::DisplayManager* display_manager = Shell::Get()->display_manager();
+  display::test::ScopedSetInternalDisplayId set_internal(display_manager,
+                                                         display_id);
+
+  const gfx::Rect bounds(0, 0, 200, 200);
+  std::unique_ptr<aura::Window> window1(CreateWindow(bounds));
+  std::unique_ptr<aura::Window> window2(CreateWindow(bounds));
+
+  split_view_controller()->SnapWindow(window1.get(), SplitViewController::LEFT);
+  split_view_controller()->SnapWindow(window2.get(),
+                                      SplitViewController::RIGHT);
+
+  const gfx::Rect bounds_window1 = window1->GetBoundsInScreen();
+  const gfx::Rect bounds_window2 = window2->GetBoundsInScreen();
+  const gfx::Rect bounds_divider =
+      split_view_divider()->GetDividerBoundsInScreen(false /* is_dragging */);
+
+  // Test that |window1| and |window2| has the same width and height after snap.
+  EXPECT_NEAR(bounds_window1.width(), bounds_window2.width(), 1);
+  EXPECT_EQ(bounds_window1.height(), bounds_window2.height());
+  EXPECT_EQ(bounds_divider.height(), bounds_window1.height());
+
+  // Test that |window1|, divider, |window2| are aligned properly.
+  EXPECT_EQ(bounds_divider.x(), bounds_window1.x() + bounds_window1.width());
+  EXPECT_EQ(bounds_window2.x(), bounds_divider.x() + bounds_divider.width());
+
+  // Drag the divider to end split view pending the snap animation.
+  const gfx::Point divider_center =
+      split_view_divider()
+          ->GetDividerBoundsInScreen(false /* is_dragging */)
+          .CenterPoint();
+  GetEventGenerator()->set_current_screen_location(divider_center);
+  GetEventGenerator()->DragMouseBy(20 - bounds_window1.width(), 0);
+  ASSERT_TRUE(split_view_controller()->InSplitViewMode());
+  ASSERT_TRUE(IsDividerAnimating());
+
+  // Change the display configuration and check that split view ends.
+  UpdateDisplay("507x500");
+  EXPECT_FALSE(split_view_controller()->InSplitViewMode());
+}
+
+// Test that if the internal screen display configuration changes during the
+// divider snap animation, and if the adjusted divider bounds place it at the
+// right edge of the screen, then split view ends.
+TEST_F(SplitViewControllerTest,
+       InternalDisplayConfigurationChangeDuringDividerSnapToRight) {
   UpdateDisplay("407x400");
   int64_t display_id = display::Screen::GetScreen()->GetPrimaryDisplay().id();
   display::DisplayManager* display_manager = Shell::Get()->display_manager();