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 28707ca7ea3a15ca95b127b2d6655fce60e624fa..704a59591a15174c78126b1a904a18f28ce9b06d 100644
--- a/ui/gfx/screen_mac.mm
+++ b/ui/gfx/screen_mac.mm
@@ -96,10 +96,15 @@ 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
@@ -109,29 +114,33 @@ 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;
+    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;
+        // Search for the associated screen and add it to our list.
+        for (NSScreen* screen in [NSScreen screens]) {
+          NSDictionary* screenDeviceDescription = [screen deviceDescription];

[Nico, 2013/10/24 15:41:27]

Can you build an id -> NSScreen map before this loop and then only do a lookup
here?

+          if (online_display == [[screenDeviceDescription
+                objectForKey:@"NSScreenNumber"] unsignedIntValue]) {
+            displays.push_back(GetDisplayForScreen(screen, false));
+          }
+        }
       }
     }
 
-    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(