Hard fail on ddc sdk build error

pkg/dev_compiler/tool/build_sdk.sh

Index: pkg/dev_compiler/tool/build_sdk.sh
diff --git a/pkg/dev_compiler/tool/build_sdk.sh b/pkg/dev_compiler/tool/build_sdk.sh
index 561f5c47450c9bbe16dd2dfa7d3f87ce0b9aa33f..e48dad15c8545805ba73f4d63ef35d70600d3682 100755
--- a/pkg/dev_compiler/tool/build_sdk.sh
+++ b/pkg/dev_compiler/tool/build_sdk.sh
@@ -9,7 +9,8 @@ dart -c tool/patch_sdk.dart tool/input_sdk gen/patched_sdk
 echo "*** Compiling SDK to JavaScript"
 
 # TODO(jmesserly): break out dart:html & friends.
-dart -c tool/build_sdk.dart \
+{ # Try
+  dart -c tool/build_sdk.dart \
     --dart-sdk gen/patched_sdk \
     --dart-sdk-summary=build \
     --summary-out lib/sdk/ddc_sdk.sum \
@@ -22,3 +23,7 @@ dart -c tool/build_sdk.dart \
     --modules=legacy \
     -o lib/js/legacy/dart_sdk.js \
     "$@" > tool/sdk_expected_errors.txt
+} || { # Catch
+  # Show errors if the sdk didn't compile.
+  cat tool/sdk_expected_errors.txt
+}