Compute and cache element NativeBehavior during resolution.

pkg/compiler/lib/src/native/behavior.dart

Index: pkg/compiler/lib/src/native/behavior.dart
diff --git a/pkg/compiler/lib/src/native/behavior.dart b/pkg/compiler/lib/src/native/behavior.dart
index daa6ddc920cee80e287765dc58fdc1b428087b71..a4e292274bed253b2b46795aa84e8debbd590537 100644
--- a/pkg/compiler/lib/src/native/behavior.dart
+++ b/pkg/compiler/lib/src/native/behavior.dart
@@ -705,13 +705,12 @@ class NativeBehavior {
     behavior._capture(type, compiler.resolution,
         isInterop: isInterop, compiler: compiler);
 
-    // TODO(sra): Optional arguments are currently missing from the
-    // DartType. This should be fixed so the following work-around can be
-    // removed.
-    method.functionSignature
-        .forEachOptionalParameter((ParameterElement parameter) {
-      behavior._escape(parameter.type, compiler.resolution);
-    });
+    for (DartType type in type.optionalParameterTypes) {
+      behavior._escape(type, compiler.resolution);
+    }
+    for (DartType type in type.namedParameterTypes) {
+      behavior._escape(type, compiler.resolution);
+    }
 
     behavior._overrideWithAnnotations(method, compiler);
     return behavior;