overview: Back and esc should not exit single splitview.

Test: added test
Bug: 950100
Change-Id: Ia05e481a15ac3c42bdfef075b5f1b930f37f3605
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1559253Reviewed-by: Xiaoqian Dai <xdai@chromium.org>
Commit-Queue: Sammie Quon <sammiequon@chromium.org>
Cr-Commit-Position: refs/heads/master@{#649265}

ash/wm/overview/overview_session.cc

@@ -758,7 +758,10 @@ void OverviewSession::OnKeyEvent(ui::KeyEvent* event) {
     case ui::VKEY_BROWSER_BACK:
       FALLTHROUGH;
     case ui::VKEY_ESCAPE:
-      CancelSelection();
+      // Cancel overview unless we're in single split mode with no overview
+      // windows.
+      if (!(IsEmpty() && Shell::Get()->IsSplitViewModeActive()))
+        CancelSelection();
       break;
     case ui::VKEY_UP:
       num_key_presses_++;

ash/wm/overview/overview_session_unittest.cc

@@ -1421,10 +1421,10 @@ TEST_F(OverviewSessionTest, BasicArrowKeyNavigation) {
   }
 }
 
-// Tests hitting the escape and back keys exit overview mode.
+// Tests hitting the escape and back keys exit overview mode, unless we're in
+// single splitview mode with no windows in overview.
 TEST_F(OverviewSessionTest, ExitOverviewWithKey) {
-  std::unique_ptr<aura::Window> window1(CreateTestWindow());
-  std::unique_ptr<aura::Window> window2(CreateTestWindow());
+  std::unique_ptr<aura::Window> window(CreateTestWindow());
 
   ToggleOverview();
   ASSERT_TRUE(overview_controller()->IsSelecting());
@@ -1435,6 +1435,18 @@ TEST_F(OverviewSessionTest, ExitOverviewWithKey) {
   ASSERT_TRUE(overview_controller()->IsSelecting());
   SendKey(ui::VKEY_BROWSER_BACK);
   EXPECT_FALSE(overview_controller()->IsSelecting());
+
+  // Tests that if we snap the only overview window, we cannot exit overview
+  // mode.
+  ToggleOverview();
+  ASSERT_TRUE(overview_controller()->IsSelecting());
+  Shell::Get()->split_view_controller()->SnapWindow(window.get(),
+                                                    SplitViewController::LEFT);
+  ASSERT_TRUE(overview_controller()->IsSelecting());
+  SendKey(ui::VKEY_ESCAPE);
+  EXPECT_TRUE(overview_controller()->IsSelecting());
+  SendKey(ui::VKEY_BROWSER_BACK);
+  EXPECT_TRUE(overview_controller()->IsSelecting());
 }
 
 // Regression test for clusterfuzz crash. https://crbug.com/920568