Stop running pub get at gclient sync time and fix build bugs

mojo/public/dart/third_party/source_span/lib/src/colors.dart

Index: mojo/public/dart/third_party/source_span/lib/src/colors.dart
diff --git a/mojo/public/dart/third_party/source_span/lib/src/colors.dart b/mojo/public/dart/third_party/source_span/lib/src/colors.dart
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index 0000000000000000000000000000000000000000..274fc92af617e0f7a06ab6c10a1d6ae95f042ef3
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+++ b/mojo/public/dart/third_party/source_span/lib/src/colors.dart
@@ -0,0 +1,13 @@
+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// Color constants used for generating messages.
+library source_span.colors;
+
+const String RED = '\u001b[31m';
+
+const String YELLOW = '\u001b[33m';
+
+const String NONE = '\u001b[0m';
+