Better tracking of provided types at call sites

lib/compiler/implementation/elements/elements.dart

Index: lib/compiler/implementation/elements/elements.dart
diff --git a/lib/compiler/implementation/elements/elements.dart b/lib/compiler/implementation/elements/elements.dart
index 61fe59aa980548d3547f7374c519d610b0ead379..58ae435cc5e9c51a95f877703dc2b81c78e83ed2 100644
--- a/lib/compiler/implementation/elements/elements.dart
+++ b/lib/compiler/implementation/elements/elements.dart
@@ -845,12 +845,15 @@ class FunctionSignature {
                     this.optionalParameterCount,
                     this.returnType);
 
-  void forEachParameter(void function(Element parameter)) {
+  void forEachRequiredParameter(void function(Element parameter)) {
     for (Link<Element> link = requiredParameters;
          !link.isEmpty();
          link = link.tail) {
       function(link.head);
     }
+  }
+
+  void forEachOptionalParameter(void function(Element parameter)) {
     for (Link<Element> link = optionalParameters;
          !link.isEmpty();
          link = link.tail) {
@@ -858,6 +861,11 @@ class FunctionSignature {
     }
   }
 
+  void forEachParameter(void function(Element parameter)) {
+    forEachRequiredParameter(function);
+    forEachOptionalParameter(function);
+  }
+
   int get parameterCount => requiredParameterCount + optionalParameterCount;
 }