Add iOS ARM64 and XCode 6.1 to default trybots.

TBR=fbarchard@google.com
BUG=libyuv:370

Review URL: https://webrtc-codereview.appspot.com/32619004

git-svn-id: http://libyuv.googlecode.com/svn/trunk@1187 16f28f9a-4ce2-e073-06de-1de4eb20be90

PRESUBMIT.py

@@ -31,7 +31,17 @@ def GetPreferredTryMasters(project, change):
     'mac_x64_rel',
     'ios',
     'ios_rel',
+    'ios_arm64',
+    'ios_arm64_rel',
     'mac_asan',
+    'mac_xcode61',
+    'mac_rel_xcode61',
+    'mac_x64_rel_xcode61',
+    'ios_xcode61',
+    'ios_rel_xcode61',
+    'ios_arm64_xcode61',
+    'ios_arm64_rel_xcode61',
+    'mac_asan_xcode61',
     'linux',
     'linux_rel',
     'linux_memcheck',