split view: Modify CanSnapInSplitview to account for divider thickness

Test: SplitViewControllerTest.SnapWindowWithMinimumSizeTest
Bug: 1019965
Change-Id: Ia31c621d18fbdcf6016f095f78aceff1fa0dd600
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1891756Reviewed-by: Xiaoqian Dai <xdai@chromium.org>
Commit-Queue: Avery Musbach <amusbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#711282}

ash/wm/splitview/split_view_controller_unittest.cc

@@ -1489,24 +1489,26 @@ TEST_P(SplitViewControllerTest, ExitTabletModeEndSplitView) {
   EXPECT_FALSE(split_view_controller()->InSplitViewMode());
 }
 
-// Tests that if a window's minimum size is larger than half of the display work
-// area's size, it can't be snapped.
+// Test that |CanSnapInSplitview| checks that the minimum size of the window
+// fits into the left or top, with the default divider position. (If the work
+// area length is odd, then the right or bottom will be one pixel larger.)
 TEST_P(SplitViewControllerTest, SnapWindowWithMinimumSizeTest) {
   const gfx::Rect bounds(0, 0, 400, 400);
   std::unique_ptr<aura::Window> window1(CreateWindow(bounds));
   EXPECT_TRUE(CanSnapInSplitview(window1.get()));
 
-  const gfx::Rect display_bounds =
-      screen_util::GetDisplayWorkAreaBoundsInScreenForActiveDeskContainer(
-          window1.get());
+  UpdateDisplay("800x600");
   aura::test::TestWindowDelegate* delegate =
       static_cast<aura::test::TestWindowDelegate*>(window1->delegate());
-  delegate->set_minimum_size(
-      gfx::Size(display_bounds.width() * 0.5f, display_bounds.height()));
+  delegate->set_minimum_size(gfx::Size(396, 0));
   EXPECT_TRUE(CanSnapInSplitview(window1.get()));
+  delegate->set_minimum_size(gfx::Size(397, 0));
+  EXPECT_FALSE(CanSnapInSplitview(window1.get()));
 
-  delegate->set_minimum_size(
-      gfx::Size(display_bounds.width() * 0.67f, display_bounds.height()));
+  UpdateDisplay("799x600");
+  delegate->set_minimum_size(gfx::Size(395, 0));
+  EXPECT_TRUE(CanSnapInSplitview(window1.get()));
+  delegate->set_minimum_size(gfx::Size(396, 0));
   EXPECT_FALSE(CanSnapInSplitview(window1.get()));
 }
 

ash/wm/splitview/split_view_utils.cc

@@ -331,8 +331,9 @@ bool CanSnapInSplitview(aura::Window* window) {
   if (!WindowState::Get(window)->CanSnap())
     return false;
 
-  // Return true if |window|'s minimum size, if any, fits into half the work
-  // area lengthwise.
+  // Return true if |window|'s minimum size, if any, fits into the left or top
+  // with the default divider position. (If the work area length is odd, then
+  // the right or bottom will be one pixel larger.)
   if (!window->delegate())
     return true;
   const gfx::Size min_size = window->delegate()->GetMinimumSize();
@@ -340,8 +341,10 @@ bool CanSnapInSplitview(aura::Window* window) {
       screen_util::GetDisplayWorkAreaBoundsInScreenForActiveDeskContainer(
           window);
   return IsCurrentScreenOrientationLandscape()
-             ? min_size.width() <= work_area.width() / 2
-             : min_size.height() <= work_area.height() / 2;
+             ? min_size.width() <=
+                   work_area.width() / 2 - kSplitviewDividerShortSideLength / 2
+             : min_size.height() <= work_area.height() / 2 -
+                                        kSplitviewDividerShortSideLength / 2;
 }
 
 void ShowAppCannotSnapToast() {