have build/test scripts automatically update baselines

tool/build_sdk.sh

Index: tool/build_sdk.sh
diff --git a/tool/build_sdk.sh b/tool/build_sdk.sh
index a665c8c1db42f1fbaed4bdb2e77e50d779fb209f..62140e217c538d3904457f629e69f323bce97c5a 100755
--- a/tool/build_sdk.sh
+++ b/tool/build_sdk.sh
@@ -17,22 +17,10 @@ fi
 # https://github.com/dart-lang/dev_compiler/issues/219
 dart -c bin/devc.dart --no-source-maps --sdk-check --force-compile -l warning \
     --dart-sdk tool/generated_sdk -o lib/runtime/ dart:mirrors \
-    > tool/generated_sdk/sdk_errors.txt || true
+    > tool/sdk_expected_errors.txt || true
 
 if [[ ! -f lib/runtime/dart/core.js ]] ; then
     echo 'core.js not found, assuming build failed.'
     echo './tool/build_sdk.sh can be run to reproduce this.'
     exit 1
 fi
-
-DIFF_ARGS="-u tool/sdk_expected_errors.txt tool/generated_sdk/sdk_errors.txt"
-
-if ! (diff $DIFF_ARGS > /dev/null) ; then
-    diff $DIFF_ARGS |\
-        sed -e "s/^\(+.*\)/\1/" |\
-        sed -e "s/^\(-.*\)/\1/"
-    echo
-    echo 'SDK errors have changed.  To update expectations, run:'
-    echo '$ cp tool/generated_sdk/sdk_errors.txt tool/sdk_expected_errors.txt'
-    exit 1
-fi