Cleaning up warnings from the analyzer.

sdk/lib/_internal/lib/js_helper.dart

Index: sdk/lib/_internal/lib/js_helper.dart
diff --git a/sdk/lib/_internal/lib/js_helper.dart b/sdk/lib/_internal/lib/js_helper.dart
index fa0fe094db6b318fe3c6071bdc35e7e53c906cb1..8be9ee592b3efcc035648b8378fdfb97d5fdd004 100644
--- a/sdk/lib/_internal/lib/js_helper.dart
+++ b/sdk/lib/_internal/lib/js_helper.dart
@@ -407,7 +407,7 @@ class ReflectionInfo {
               FIRST_DEFAULT_ARGUMENT, parameter, requiredParameterCount);
   }
 
-  @NoInline
+  @NoInline()
   computeFunctionRti(jsConstructor) {
     if (JS('bool', 'typeof # == "number"', functionType)) {
       return getMetadata(functionType);
@@ -2173,12 +2173,12 @@ class BoundClosure extends TearOffClosure {
     return receiverHashCode ^ Primitives.objectHashCode(_target);
   }
 
-  @NoInline
+  @NoInline()
   static selfOf(BoundClosure closure) => closure._self;
 
   static targetOf(BoundClosure closure) => closure._target;
 
-  @NoInline
+  @NoInline()
   static receiverOf(BoundClosure closure) => closure._receiver;
 
   static nameOf(BoundClosure closure) => closure._name;
@@ -2695,7 +2695,7 @@ class RuntimeFunctionType extends RuntimeType {
 
   @NoInline() @NoSideEffects()
   _assertCheck(expression) {
-    if (inAssert) return;
+    if (inAssert) return null;
     inAssert = true; // Don't try to check this library itself.
     try {
       // Type inferrer don't think this is called with dynamic arguments.