diff --git a/build/common.gypi b/build/common.gypi
index feff71683dd0db..a78095ea06f336 100644
--- a/build/common.gypi
+++ b/build/common.gypi
@@ -1331,7 +1331,7 @@
     # Control which version of clang to use when building for iOS.  If set to
     # '1', uses the version of clang that ships with Xcode.  If set to '0', uses
     # the version of clang that ships with the Chromium source.  This variable
-    # is automatically set to '1' when using the Xcode generator.
+    # is automatically set to '1' in Official builds.
     'clang_xcode%': 0,
 
     # These two variables can be set in GYP_DEFINES while running
@@ -5352,6 +5352,9 @@
             ['clang_xcode==1', {
               'WARNING_CFLAGS': [
                 '-Wno-unknown-warning-option',
+                # It's not possible to achieve nullability completeness before
+                # all builders are running Xcode 7. crbug.com/499809
+                '-Wno-nullability-completeness',
               ],
             }],
 
diff --git a/testing/iossim/iossim.mm b/testing/iossim/iossim.mm
index 933a183c0b73b3..4d557ac8a875ac 100644
--- a/testing/iossim/iossim.mm
+++ b/testing/iossim/iossim.mm
@@ -632,7 +632,18 @@ - (void)session:(DTiPhoneSimulatorSession*)session
 // valid.
 DTiPhoneSimulatorSystemRoot* BuildSystemRoot(NSString* sdkVersion) {
   Class systemRootClass = FindClassByName(@"DTiPhoneSimulatorSystemRoot");
+#if defined(IOSSIM_USE_XCODE_6)
+  Class simRuntimeClass = FindClassByName(@"SimRuntime");
+  NSArray* sorted =
+      [[simRuntimeClass supportedRuntimes] sortedArrayUsingDescriptors:@[
+        [NSSortDescriptor sortDescriptorWithKey:@"version" ascending:YES]
+      ]];
+  NSString* versionString = [[sorted lastObject] versionString];
+  DTiPhoneSimulatorSystemRoot* systemRoot =
+      [systemRootClass rootWithSDKVersion:versionString];
+#else
   DTiPhoneSimulatorSystemRoot* systemRoot = [systemRootClass defaultRoot];
+#endif
   if (sdkVersion)
     systemRoot = [systemRootClass rootWithSDKVersion:sdkVersion];
 
@@ -666,7 +677,7 @@ - (void)session:(DTiPhoneSimulatorSession*)session
 #if defined(IOSSIM_USE_XCODE_6)
     Class simDeviceTypeClass = FindClassByName(@"SimDeviceType");
     id simDeviceType =
-        [simDeviceTypeClass supportedDeviceTypesByName][deviceName];
+        [simDeviceTypeClass supportedDeviceTypesByAlias][deviceName];
     Class simRuntimeClass = FindClassByName(@"SimRuntime");
     NSString* identifier = systemRoot.runtime.identifier;
     id simRuntime = [simRuntimeClass supportedRuntimesByIdentifier][identifier];
@@ -956,7 +967,7 @@ int main(int argc, char* const argv[]) {
   if (IsRunningWithXcode6OrLater()) {
 #if defined(IOSSIM_USE_XCODE_6)
     Class simDeviceTypeClass = FindClassByName(@"SimDeviceType");
-    if ([simDeviceTypeClass supportedDeviceTypesByName][deviceName] == nil) {
+    if ([simDeviceTypeClass supportedDeviceTypesByAlias][deviceName] == nil) {
       LogError(@"Invalid device name: %@.", deviceName);
       PrintSupportedDevices();
       exit(kExitInvalidArguments);