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

mojo/public/dart/third_party/path/lib/src/path_exception.dart

Index: mojo/public/dart/third_party/path/lib/src/path_exception.dart
diff --git a/mojo/public/dart/third_party/path/lib/src/path_exception.dart b/mojo/public/dart/third_party/path/lib/src/path_exception.dart
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index 0000000000000000000000000000000000000000..49bd268e4d5382de9d0bc547946a19589be409d8
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+++ b/mojo/public/dart/third_party/path/lib/src/path_exception.dart
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+// Copyright (c) 2013, 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.
+
+library path.path_exception;
+
+/// An exception class that's thrown when a path operation is unable to be
+/// computed accurately.
+class PathException implements Exception {
+  String message;
+
+  PathException(this.message);
+
+  String toString() => "PathException: $message";
+}