Fix iossim's support for retina devices.

testing/iossim/iossim.mm

Index: testing/iossim/iossim.mm
diff --git a/testing/iossim/iossim.mm b/testing/iossim/iossim.mm
index 7d5dbf872e93cbc9c7e1155fefdbef3cd9caef07..ac03dcd1b15baa29a76343c46b8c3e7597defada 100644
--- a/testing/iossim/iossim.mm
+++ b/testing/iossim/iossim.mm
@@ -491,12 +491,11 @@ BOOL InitializeSimulatorUserHome(NSString* userHomePath, NSString* deviceName) {
 
   // Set the device to simulate. Note that the iOS Simulator must not be running
   // for this setting to take effect.
-  NSMutableDictionary* plistDict =
-      [NSMutableDictionary dictionaryWithObject:deviceName
-                                         forKey:@"SimulateDevice"];
-  NSString* plistPath = @"Library/Preferences/com.apple.iphonesimulator.plist";
-  [plistDict writeToFile:[userHomePath stringByAppendingPathComponent:plistPath]
-              atomically:YES];
+  CFStringRef iPhoneSimulatorAppID = CFSTR("com.apple.iphonesimulator");
+  CFPreferencesSetAppValue(CFSTR("SimulateDevice"),
+                           deviceName,
+                           iPhoneSimulatorAppID);
+  CFPreferencesAppSynchronize(iPhoneSimulatorAppID);
 
   // Update the environment to use the specified directory as the user home
   // directory.