Don't run pub in checked mode in the built SDK.

sdk/bin/pub

 #!/bin/bash
 # Copyright (c) 2012, 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.
 
 # Run pub.dart on the Dart VM. This script assumes the Dart SDK's directory
 # structure.
 
 # Setting BIN_DIR this way is ugly, but is needed to handle the case where
 # dart-sdk/bin has been symlinked to. On MacOS, readlink doesn't work
 # with this case.
 BIN_DIR="$(cd "${0%/*}" ; pwd -P)"
 SDK_DIR="$(cd "${BIN_DIR}/.." ; pwd -P)"
 
 SNAPSHOT="$BIN_DIR/snapshots/pub.dart.snapshot"
 
 if test -f "$SNAPSHOT"; then
   # We are running the snapshot in the built SDK.
   DART="$BIN_DIR/dart"
-  exec "$DART" "--checked" "$SNAPSHOT" "$@"
+  exec "$DART" "$SNAPSHOT" "$@"
 else
   # We are running pub from source in the development repo.
   if [ -z "$DART_CONFIGURATION" ];
   then
     DART_CONFIGURATION="ReleaseIA32"
   fi
 
   if [[ `uname` == 'Darwin' ]];
   then
     BUILD_DIR="$SDK_DIR/../xcodebuild/$DART_CONFIGURATION"
   else
     BUILD_DIR="$SDK_DIR/../out/$DART_CONFIGURATION"
   fi
 
   # Use the Dart binary in the built SDK so pub can find the version file next
   # to it.
   DART="$BUILD_DIR/dart-sdk/bin/dart"
   PACKAGES_DIR="$BUILD_DIR/packages/"
 
   PUB="$SDK_DIR/lib/_internal/pub/bin/pub.dart"
 
-  exec "$DART" "--checked" "--package-root=$PACKAGES_DIR" "$PUB" "$@"
+  exec "$DART" "--package-root=$PACKAGES_DIR" "$PUB" "$@"
 fi