Update Dart SDK to 1.12.0-dev.3.1

sky/tools/skyanalyzer

 #!/usr/bin/env python
 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import argparse
 import os
 import re
 import subprocess
 import sys
 
 from skypy.url_mappings import URLMappings
 
 SKY_TOOLS_DIR = os.path.dirname(os.path.abspath(__file__))
 SKY_ROOT = os.path.dirname(SKY_TOOLS_DIR)
 SRC_ROOT = os.path.dirname(SKY_ROOT)
 
 _IGNORED_PATTERNS = [
   # Ignored because they're not indicative of specific errors.
   re.compile(r'^$'),
   re.compile(r'^Analyzing \['),
   re.compile(r'^No issues found'),
   re.compile(r'^[0-9]+ errors? and [0-9]+ warnings? found.'),
   re.compile(r'^([0-9]+|No) (error|warning|issue)s? found.'),
 
+  # Ignore analyzer status output.
+  re.compile(r'^[0-9]+ errors, [0-9]+ warnings and [0-9]+ hints found.'),
+
   # Ignored because they don't affect Sky code
   re.compile(r'\[hint\] When compiled to JS, this test might return true when the left hand side is an int'),
 
   # TODO: Remove once sdk-extensions are in place
   re.compile(r'^\[error\] Native functions can only be declared in'),
 
   # TODO: Fix all the warnings in the mojo packages
   re.compile(r'.*/dart-pkg/mojom/'),
   re.compile(r'.*/dart-pkg/mojo/'),
   re.compile(r'.*/mojo/public/dart/'),
@@ skipping 36 matching lines @@
           print >> sys.stderr, error
         # Propagate analyzer error code.
         return e.returncode
     # If we do not have any errors left after filtering, return 0.
     if args.congratulate:
       print >> sys.stdout, "No analyzer warnings!"
     return 0
 
 if __name__ == '__main__':
     sys.exit(main())