Dart2js deferred loading. Follow types of functions when calculating dependencies.

pkg/compiler/lib/src/js_backend/custom_elements_analysis.dart

Index: pkg/compiler/lib/src/js_backend/custom_elements_analysis.dart
diff --git a/pkg/compiler/lib/src/js_backend/custom_elements_analysis.dart b/pkg/compiler/lib/src/js_backend/custom_elements_analysis.dart
index 9a5c8e987940a9ec62bb27bc9291ab808012f7ee..99c46ca8a3461756540770966cb1519263428a79 100644
--- a/pkg/compiler/lib/src/js_backend/custom_elements_analysis.dart
+++ b/pkg/compiler/lib/src/js_backend/custom_elements_analysis.dart
@@ -193,6 +193,7 @@ class CustomElementsAnalysisJoin {
       if (member.isGenerativeConstructor) {
         // Ignore constructors that cannot be called with zero arguments.
         FunctionElement constructor = member;
+        constructor.computeSignature(compiler);
         FunctionSignature parameters = constructor.functionSignature;
         if (parameters.requiredParameterCount == 0) {
           result.add(member);