Set an exit code when exiting build_sdk_summary in error.

pkg/analyzer/tool/summary/build_sdk_summary.dart

Index: pkg/analyzer/tool/summary/build_sdk_summary.dart
diff --git a/pkg/analyzer/tool/summary/build_sdk_summary.dart b/pkg/analyzer/tool/summary/build_sdk_summary.dart
index 738e0a19aee09b5c958ad8ef55ee10854e907465..6fe7bd11bf7b507e454b047359cabd488f75ddf4 100644
--- a/pkg/analyzer/tool/summary/build_sdk_summary.dart
+++ b/pkg/analyzer/tool/summary/build_sdk_summary.dart
@@ -12,7 +12,7 @@ import 'package:analyzer/src/summary/summarize_elements.dart';
 main(List<String> args) {
   if (args.length < 1 || args.length > 2) {
     _printUsage();
-    return;
+    exit(1);

[kevmoo, 2016/02/03 19:22:07]

consider setting exitCode = 1 and return.

exit(n) borks Observatory – so you can't do code coverage, etc.

[Paul Berry, 2016/02/04 13:27:34]

Done.

   }
   //
   // Prepare output file path.
@@ -21,7 +21,7 @@ main(List<String> args) {
   if (FileSystemEntity.isDirectorySync(outputFilePath)) {
     print("'$outputFilePath' is a directory.");
     _printUsage();
-    return;
+    exit(1);
   }
   //
   // Prepare SDK path.
@@ -32,7 +32,7 @@ main(List<String> args) {
     if (!FileSystemEntity.isDirectorySync('$sdkPath/lib')) {
       print("'$sdkPath/lib' does not exist.");
       _printUsage();
-      return;
+      exit(1);
     }
   } else {
     sdkPath = DirectoryBasedDartSdk.defaultSdkDirectory.getAbsolutePath();