cros: record nums of window restored for persistent restore

changes:
According to the design doc: go/cros-persistent-window-bounds, add UMA
for recording the number of windows restored for persistent window
restore in multi-display scenario.

Bug: 805046
Test: tested on device, checked chrome://histograms and added test coverage
Change-Id: I4f8c815c1b88dd605a02b509b27311d567998da1
Reviewed-on: https://chromium-review.googlesource.com/942186Reviewed-by: Ahmed Fakhry <afakhry@chromium.org>
Reviewed-by: Mark Pearson <mpearson@chromium.org>
Commit-Queue: Qiang Xu <warx@google.com>
Cr-Commit-Position: refs/heads/master@{#540339}

ash/display/persistent_window_controller.cc

@@ -11,6 +11,7 @@
 #include "ash/wm/mru_window_tracker.h"
 #include "ash/wm/window_state.h"
 #include "base/command_line.h"
+#include "base/metrics/histogram_macros.h"
 #include "ui/display/manager/display_manager.h"
 #include "ui/display/screen.h"
 
@@ -49,6 +50,7 @@ void MaybeRestorePersistentWindowBounds() {
     return;
 
   display::Screen* screen = display::Screen::GetScreen();
+  int window_restored_count = 0;
   for (auto* window : GetWindowList()) {
     wm::WindowState* window_state = wm::GetWindowState(window);
     if (!window_state->persistent_window_info())
@@ -80,11 +82,21 @@ void MaybeRestorePersistentWindowBounds() {
     window->SetBoundsInScreen(persistent_window_bounds, display);
     // Reset persistent window info everytime the window bounds have restored.
     window_state->ResetPersistentWindowInfo();
+
+    ++window_restored_count;
+  }
+
+  if (window_restored_count != 0) {
+    UMA_HISTOGRAM_COUNTS_100(
+        PersistentWindowController::kNumOfWindowsRestoredHistogramName,
+        window_restored_count);
   }
 }
 
 }  // namespace
 
+constexpr char PersistentWindowController::kNumOfWindowsRestoredHistogramName[];
+
 PersistentWindowController::PersistentWindowController() {
   display::Screen::GetScreen()->AddObserver(this);
   Shell::Get()->session_controller()->AddObserver(this);

ash/display/persistent_window_controller.h

@@ -20,6 +20,10 @@ class ASH_EXPORT PersistentWindowController
       public SessionObserver,
       public WindowTreeHostManager::Observer {
  public:
+  // Public so it can be used by unit tests.
+  constexpr static char kNumOfWindowsRestoredHistogramName[] =
+      "Ash.PersistentWindow.NumOfWindowsRestored";
+
   PersistentWindowController();
   ~PersistentWindowController() override;
 

ash/display/persistent_window_controller_unittest.cc

@@ -13,6 +13,7 @@
 #include "ash/wm/window_state.h"
 #include "ash/wm/window_util.h"
 #include "base/command_line.h"
+#include "base/test/histogram_tester.h"
 
 using session_manager::SessionState;
 
@@ -355,4 +356,42 @@ TEST_F(PersistentWindowControllerTest, ReconnectOnLockScreen) {
   EXPECT_EQ(gfx::Rect(501, 0, 200, 100), w2->GetBoundsInScreen());
 }
 
+TEST_F(PersistentWindowControllerTest, RecordNumOfWindowsRestored) {
+  UpdateDisplay("0+0-500x500,0+501-500x500");
+  aura::Window* w1 =
+      CreateTestWindowInShellWithBounds(gfx::Rect(200, 0, 100, 200));
+  aura::Window* w2 =
+      CreateTestWindowInShellWithBounds(gfx::Rect(501, 0, 200, 100));
+  EXPECT_EQ(gfx::Rect(200, 0, 100, 200), w1->GetBoundsInScreen());
+  EXPECT_EQ(gfx::Rect(501, 0, 200, 100), w2->GetBoundsInScreen());
+
+  const int64_t primary_id = WindowTreeHostManager::GetPrimaryDisplayId();
+  const int64_t secondary_id = display_manager()->GetSecondaryDisplay().id();
+
+  display::ManagedDisplayInfo primary_info =
+      display_manager()->GetDisplayInfo(primary_id);
+  display::ManagedDisplayInfo secondary_info =
+      display_manager()->GetDisplayInfo(secondary_id);
+
+  // Disconnects secondary display.
+  std::vector<display::ManagedDisplayInfo> display_info_list;
+  display_info_list.push_back(primary_info);
+  display_manager()->OnNativeDisplaysChanged(display_info_list);
+  EXPECT_EQ(gfx::Rect(200, 0, 100, 200), w1->GetBoundsInScreen());
+  EXPECT_EQ(gfx::Rect(1, 0, 200, 100), w2->GetBoundsInScreen());
+
+  base::HistogramTester histogram_tester;
+  histogram_tester.ExpectTotalCount(
+      PersistentWindowController::kNumOfWindowsRestoredHistogramName, 0);
+
+  // Reconnects secondary display.
+  display_info_list.push_back(secondary_info);
+  display_manager()->OnNativeDisplaysChanged(display_info_list);
+  EXPECT_EQ(gfx::Rect(200, 0, 100, 200), w1->GetBoundsInScreen());
+  EXPECT_EQ(gfx::Rect(501, 0, 200, 100), w2->GetBoundsInScreen());
+
+  histogram_tester.ExpectTotalCount(
+      PersistentWindowController::kNumOfWindowsRestoredHistogramName, 1);
+}
+
 }  // namespace ash

tools/metrics/histograms/histograms.xml

@@ -3477,6 +3477,15 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Ash.PersistentWindow.NumOfWindowsRestored">
+  <owner>warx@chromium.org</owner>
+  <summary>
+    The number of windows restored in multi-display scenario, such as due to
+    disconnecting and reconnecting display, enabling and disabling mirror mode,
+    entering and leaving dock mode. Zero is not recorded.
+  </summary>
+</histogram>
+
 <histogram name="Ash.PowerButtonScreenshot.DelayBetweenAccelKeyPressed"
     units="ms">
   <owner>warx@chromium.org</owner>