Listen to Display reconfiguration and notify DisplayObservers on Mac.

ui/gfx/screen_mac.mm

Index: ui/gfx/screen_mac.mm
diff --git a/ui/gfx/screen_mac.mm b/ui/gfx/screen_mac.mm
index bbf29d335432be494224cbe8fbc1b0c9ce47d44a..11a8b3a4d54a1760c35c2ef0aae4434fdf311124 100644
--- a/ui/gfx/screen_mac.mm
+++ b/ui/gfx/screen_mac.mm
@@ -11,10 +11,16 @@
 
 #include "base/logging.h"
 #include "base/mac/sdk_forward_declarations.h"
+#include "base/timer/timer.h"
 #include "ui/gfx/display.h"
+#include "ui/gfx/display_change_notifier.h"
 
 namespace {
 
+// The delay to handle the display configuration changes.
+// See comments in ScreenMac::HandleDisplayReconfiguration.
+const int64 kConfigureDelayMs = 500;
+
 gfx::Rect ConvertCoordinateSystem(NSRect ns_rect) {
   // Primary monitor is defined as the monitor with the menubar,
   // which is always at index 0.
@@ -78,7 +84,12 @@ gfx::Display GetDisplayForScreen(NSScreen* screen) {
 
 class ScreenMac : public gfx::Screen {
  public:
-  ScreenMac() {}
+  ScreenMac() {
+    displays_ = BuildDisplaysFromQuartz();
+
+    CGDisplayRegisterReconfigurationCallback(
+        ScreenMac::DisplayReconfigurationCallBack, this);
+  }
 
   virtual bool IsDIPEnabled() OVERRIDE {
     return true;
@@ -109,52 +120,7 @@ class ScreenMac : public gfx::Screen {
   }
 
   virtual std::vector<gfx::Display> GetAllDisplays() const OVERRIDE {
-    // Don't just return all online displays.  This would include displays
-    // that mirror other displays, which are not desired in this list.  It's
-    // tempting to use the count returned by CGGetActiveDisplayList, but active
-    // displays exclude sleeping displays, and those are desired.
-
-    // It would be ridiculous to have this many displays connected, but
-    // CGDirectDisplayID is just an integer, so supporting up to this many
-    // doesn't hurt.
-    CGDirectDisplayID online_displays[128];
-    CGDisplayCount online_display_count = 0;
-    if (CGGetOnlineDisplayList(arraysize(online_displays),
-                              online_displays,
-                              &online_display_count) != kCGErrorSuccess) {
-      return std::vector<gfx::Display>(1, GetPrimaryDisplay());
-    }
-
-    typedef std::map<int64, NSScreen*> ScreenIdsToScreensMap;
-    ScreenIdsToScreensMap screen_ids_to_screens;
-    for (NSScreen* screen in [NSScreen screens]) {
-      NSDictionary* screen_device_description = [screen deviceDescription];
-      int64 screen_id = [[screen_device_description
-        objectForKey:@"NSScreenNumber"] unsignedIntValue];
-      screen_ids_to_screens[screen_id] = screen;
-    }
-
-    std::vector<gfx::Display> displays;
-    for (CGDisplayCount online_display_index = 0;
-        online_display_index < online_display_count;
-        ++online_display_index) {
-      CGDirectDisplayID online_display = online_displays[online_display_index];
-      if (CGDisplayMirrorsDisplay(online_display) == kCGNullDirectDisplay) {
-        // If this display doesn't mirror any other, include it in the list.
-        // The primary display in a mirrored set will be counted, but those that
-        // mirror it will not be.
-        ScreenIdsToScreensMap::iterator foundScreen =
-          screen_ids_to_screens.find(online_display);
-        if (foundScreen != screen_ids_to_screens.end()) {
-            displays.push_back(GetDisplayForScreen(foundScreen->second));
-        }
-      }
-    }
-
-    if (!displays.size())
-      return std::vector<gfx::Display>(1, GetPrimaryDisplay());
-
-    return displays;
+    return displays_;
   }
 
   virtual gfx::Display GetDisplayNearestWindow(
@@ -202,14 +168,105 @@ class ScreenMac : public gfx::Screen {
   }
 
   virtual void AddObserver(gfx::DisplayObserver* observer) OVERRIDE {
-    // TODO(oshima): crbug.com/122863.
+    change_notifier_.AddObserver(observer);
   }
 
   virtual void RemoveObserver(gfx::DisplayObserver* observer) OVERRIDE {
-    // TODO(oshima): crbug.com/122863.
+    change_notifier_.RemoveObserver(observer);
+  }
+
+  static void DisplayReconfigurationCallBack(CGDirectDisplayID display,
+                                             CGDisplayChangeSummaryFlags flags,
+                                             void* userInfo) {
+    if (flags & kCGDisplayBeginConfigurationFlag)
+      return;
+
+    static_cast<ScreenMac*>(userInfo)->HandleDisplayReconfiguration();
+  }
+
+  void HandleDisplayReconfiguration() {
+    // Given that we need to rebuild the list of displays, we want to coalesce
+    // the events. For that, we use a timer that will be reset every time we get
+    // a new event and will be fulfilled kConfigureDelayMs after the latest.
+    if (configure_timer_.get() && configure_timer_->IsRunning()) {
+      configure_timer_->Reset();
+      return;
+    }
+
+    configure_timer_.reset(new base::OneShotTimer<ScreenMac>());
+    configure_timer_->Start(
+        FROM_HERE,
+        base::TimeDelta::FromMilliseconds(kConfigureDelayMs),
+        this,
+        &ScreenMac::ConfigureTimerFired);
   }
 
  private:
+  void ConfigureTimerFired() {
+    std::vector<gfx::Display> old_displays = displays_;
+    displays_ = BuildDisplaysFromQuartz();
+
+    change_notifier_.NotifyDisplaysChanged(old_displays, displays_);
+  }
+
+  std::vector<gfx::Display> BuildDisplaysFromQuartz() const {
+    // Don't just return all online displays.  This would include displays
+    // that mirror other displays, which are not desired in this list.  It's
+    // tempting to use the count returned by CGGetActiveDisplayList, but active
+    // displays exclude sleeping displays, and those are desired.
+
+    // It would be ridiculous to have this many displays connected, but
+    // CGDirectDisplayID is just an integer, so supporting up to this many
+    // doesn't hurt.
+    CGDirectDisplayID online_displays[128];
+    CGDisplayCount online_display_count = 0;
+    if (CGGetOnlineDisplayList(arraysize(online_displays),
+                              online_displays,
+                              &online_display_count) != kCGErrorSuccess) {
+      return std::vector<gfx::Display>(1, GetPrimaryDisplay());
+    }
+
+    typedef std::map<int64, NSScreen*> ScreenIdsToScreensMap;
+    ScreenIdsToScreensMap screen_ids_to_screens;
+    for (NSScreen* screen in [NSScreen screens]) {
+      NSDictionary* screen_device_description = [screen deviceDescription];
+      int64 screen_id = [[screen_device_description
+        objectForKey:@"NSScreenNumber"] unsignedIntValue];
+      screen_ids_to_screens[screen_id] = screen;
+    }
+
+    std::vector<gfx::Display> displays;
+    for (CGDisplayCount online_display_index = 0;
+        online_display_index < online_display_count;
+        ++online_display_index) {
+      CGDirectDisplayID online_display = online_displays[online_display_index];
+      if (CGDisplayMirrorsDisplay(online_display) == kCGNullDirectDisplay) {
+        // If this display doesn't mirror any other, include it in the list.
+        // The primary display in a mirrored set will be counted, but those that
+        // mirror it will not be.
+        ScreenIdsToScreensMap::iterator foundScreen =
+          screen_ids_to_screens.find(online_display);
+        if (foundScreen != screen_ids_to_screens.end()) {
+            displays.push_back(GetDisplayForScreen(foundScreen->second));
+        }
+      }
+    }
+
+    if (!displays.size())
+      return std::vector<gfx::Display>(1, GetPrimaryDisplay());
+
+    return displays;
+  }
+
+  // The displays currently attached to the device.
+  std::vector<gfx::Display> displays_;
+
+  // The timer to delay configuring outputs. See also the comments in
+  // HandleDisplayReconfiguration().
+  scoped_ptr<base::OneShotTimer<ScreenMac> > configure_timer_;
+
+  gfx::DisplayChangeNotifier change_notifier_;
+
   DISALLOW_COPY_AND_ASSIGN(ScreenMac);
 };