capture mode: exclude home screen window from window capture mode.

Bug: 1160367
Change-Id: If3ebbe49d221e41bd19f495fcadb5881a0252e1e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2600043Reviewed-by: Ahmed Fakhry <afakhry@chromium.org>
Commit-Queue: Xiaoqian Dai <xdai@chromium.org>
Cr-Commit-Position: refs/heads/master@{#838699}

ash/capture_mode/capture_mode_unittests.cc

@@ -19,6 +19,7 @@
 #include "ash/display/cursor_window_controller.h"
 #include "ash/display/screen_orientation_controller_test_api.h"
 #include "ash/display/window_tree_host_manager.h"
+#include "ash/home_screen/home_screen_controller.h"
 #include "ash/magnifier/magnifier_glass.h"
 #include "ash/public/cpp/ash_features.h"
 #include "ash/root_window_controller.h"
@@ -1925,9 +1926,10 @@ TEST_F(CaptureModeTest, TabletTouchCaptureLabelWidgetWindowMode) {
   event_generator->PressTouch();
   event_generator->ReleaseTouch();
 
-  // There are no windows so the window finder algorithm will find the app list
-  // window and take a picture of that, ending capture mode.
-  EXPECT_FALSE(controller->IsActive());
+  // There are no windows and home screen window is excluded from window capture
+  // mode, so capture mode will still remain active.
+  EXPECT_TRUE(Shell::Get()->home_screen_controller()->IsHomeScreenVisible());
+  EXPECT_TRUE(controller->IsActive());
 }
 
 // Tests that after rotating a display, the capture session widgets are updated

ash/capture_mode/capture_window_observer.cc

@@ -5,6 +5,8 @@
 #include "ash/capture_mode/capture_window_observer.h"
 
 #include "ash/capture_mode/capture_mode_session.h"
+#include "ash/home_screen/home_screen_controller.h"
+#include "ash/home_screen/home_screen_delegate.h"
 #include "ash/public/cpp/shell_window_ids.h"
 #include "ash/public/cpp/window_finder.h"
 #include "ash/shell.h"
@@ -40,6 +42,14 @@ void CaptureWindowObserver::UpdateSelectedWindowAtPosition(
     window = nullptr;
   }
 
+  // Don't capture home screen window.
+  if (window && window == Shell::Get()
+                              ->home_screen_controller()
+                              ->delegate()
+                              ->GetHomeScreenWindow()) {
+    window = nullptr;
+  }
+
   // Stop observing the current selected window if there is one.
   StopObserving();
   if (window)