Implement GetAllDisplays() for the Mac screen backend

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 f63bd306cd8bb19273def02b0ebbfe24ddf97b53..51c0b665b7e34274b98cf4c2d3386898af8c98f3 100644
--- a/ui/gfx/screen_mac.mm
+++ b/ui/gfx/screen_mac.mm
@@ -7,6 +7,8 @@
 #import <ApplicationServices/ApplicationServices.h>
 #import <Cocoa/Cocoa.h>
 
+#include <map>
+
 #include "base/logging.h"
 #include "base/mac/sdk_forward_declarations.h"
 #include "ui/gfx/display.h"
@@ -97,10 +99,15 @@ class ScreenMac : public gfx::Screen {
   }
 
   virtual int GetNumDisplays() const OVERRIDE {
-    // Don't just return the number of online displays.  It includes displays
-    // that mirror other displays, which are not desired in the count.  It's
+    return GetAllDisplays().size();
+
+  }
+
+  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 in the count.
+    // 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
@@ -110,29 +117,39 @@ class ScreenMac : public gfx::Screen {
     if (CGGetOnlineDisplayList(arraysize(online_displays),
                               online_displays,
                               &online_display_count) != kCGErrorSuccess) {
-      // 1 is a reasonable assumption.
-      return 1;
+      return std::vector<gfx::Display>(1, GetPrimaryDisplay());
     }
 
-    int display_count = 0;
+    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 count.
+        // 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.
-        ++display_count;
+        ScreenIdsToScreensMap::iterator foundScreen =
+          screen_ids_to_screens.find(online_display);
+        if (foundScreen != screen_ids_to_screens.end()) {
+            displays.push_back(GetDisplayForScreen(foundScreen->second));
+        }
       }
     }
 
-    return display_count;
-  }
+    if (!displays.size())
+      return std::vector<gfx::Display>(1, GetPrimaryDisplay());
 
-  virtual std::vector<gfx::Display> GetAllDisplays() const OVERRIDE {
-    NOTIMPLEMENTED();
-    return std::vector<gfx::Display>(1, GetPrimaryDisplay());
+    return displays;
   }
 
   virtual gfx::Display GetDisplayNearestWindow(