Add --analyze-signatures-only option to dart2js

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

Index: sdk/lib/_internal/compiler/implementation/compiler.dart
diff --git a/sdk/lib/_internal/compiler/implementation/compiler.dart b/sdk/lib/_internal/compiler/implementation/compiler.dart
index bdda72eb0990676d3ced0d3081898a7ac6547643..21755e7e5a2feb2f249a2a4bbcdb7e05c0c3523f 100644
--- a/sdk/lib/_internal/compiler/implementation/compiler.dart
+++ b/sdk/lib/_internal/compiler/implementation/compiler.dart
@@ -216,6 +216,11 @@ abstract class Compiler implements DiagnosticListener {
   final int maxConcreteTypeSize;
   final bool analyzeAll;
   final bool analyzeOnly;
+  /**
+   * If true, skip analysis of method bodies and field initializers. Can only
+   * be used when [analyzeOnly] is set.
+   */
+  final bool analyzeSignaturesOnly;
   final bool enableNativeLiveTypeAnalysis;
   final bool rejectDeprecatedFeatures;
   final bool checkDeprecationInSdk;
@@ -354,6 +359,7 @@ abstract class Compiler implements DiagnosticListener {
             bool disallowUnsafeEval: false,
             this.analyzeAll: false,
             this.analyzeOnly: false,
+            this.analyzeSignaturesOnly: false,
             this.rejectDeprecatedFeatures: false,
             this.checkDeprecationInSdk: false,
             this.preserveComments: false,