Add --analyze-signatures-only option to dart2js

sdk/lib/_internal/compiler/implementation/apiimpl.dart

Index: sdk/lib/_internal/compiler/implementation/apiimpl.dart
diff --git a/sdk/lib/_internal/compiler/implementation/apiimpl.dart b/sdk/lib/_internal/compiler/implementation/apiimpl.dart
index c9759f3cfa7a411599bfcb5a313db29fa83f8234..9fe63b67757dc6b0f230d93071ddf38706bf37ed 100644
--- a/sdk/lib/_internal/compiler/implementation/apiimpl.dart
+++ b/sdk/lib/_internal/compiler/implementation/apiimpl.dart
@@ -44,6 +44,8 @@ class Compiler extends leg.Compiler {
             disallowUnsafeEval: hasOption(options, '--disallow-unsafe-eval'),
             analyzeAll: hasOption(options, '--analyze-all'),
             analyzeOnly: hasOption(options, '--analyze-only'),
+            analyzeSignaturesOnly:
+                hasOption(options, '--analyze-signatures-only'),
             rejectDeprecatedFeatures:
                 hasOption(options, '--reject-deprecated-language-features'),
             checkDeprecationInSdk:
@@ -59,6 +61,10 @@ class Compiler extends leg.Compiler {
     if (packageRoot != null && !packageRoot.path.endsWith("/")) {
       throw new ArgumentError("packageRoot must end with a /");
     }
+    if (analyzeSignaturesOnly && !analyzeOnly) {

[ahe, 2013/03/05 14:32:59]

How about --analyze-signatures-only implies --analyze-only?

[Johnni Winther, 2013/03/05 16:52:49]

Done.

+      throw new ArgumentError("--analyze-signatures-only can only "
+                              "be used together with --analyze-only");
+    }
   }
 
   static List<String> getStrips(List<String> options) {