dart2js: fix for https://github.com/dart-lang/sdk/issues/24412

sdk/lib/_internal/js_runtime/lib/js_helper.dart

Index: sdk/lib/_internal/js_runtime/lib/js_helper.dart
diff --git a/sdk/lib/_internal/js_runtime/lib/js_helper.dart b/sdk/lib/_internal/js_runtime/lib/js_helper.dart
index 000753264a5a14a5d0146b9800c9770b9ec1c2c5..e8b0a6bded4316b37da9f1b771d5c253647ef2c7 100644
--- a/sdk/lib/_internal/js_runtime/lib/js_helper.dart
+++ b/sdk/lib/_internal/js_runtime/lib/js_helper.dart
@@ -845,6 +845,7 @@ class Primitives {
   /// Returns the type of [object] as a string (including type arguments).
   ///
   /// In minified mode, uses the unminified names if available.
+  @NoInline()
   static String objectTypeName(Object object) {
     return formatType(_objectRawTypeName(object), getRuntimeTypeInfo(object));
   }
@@ -867,9 +868,8 @@ class Primitives {
     }
 
     if (name == null ||
-        identical(interceptor,
-            JS_INTERCEPTOR_CONSTANT(UnknownJavaScriptObject)) ||
-        identical(interceptor, JS_INTERCEPTOR_CONSTANT(Interceptor))) {
+        identical(interceptor, JS_INTERCEPTOR_CONSTANT(Interceptor)) ||
+        object is UnknownJavaScriptObject) {
       // Try to do better.  If we do not find something better, leave the name
       // as 'UnknownJavaScriptObject' or 'Interceptor' (or the minified name).
       //
@@ -885,7 +885,6 @@ class Primitives {
       // Try the [constructorNameFallback]. This gets the constructor name for
       // any browser (used by [getNativeInterceptor]).
       String dispatchName = constructorNameFallback(object);
-      if (name == null) name = dispatchName;
       if (dispatchName == 'Object') {
         // Try to decompile the constructor by turning it into a string and get
         // the name out of that. If the decompiled name is a string containing
@@ -900,11 +899,16 @@ class Primitives {
             name = decompiledName;
           }
         }
+        if (name == null) name = dispatchName;
       } else {
         name = dispatchName;
       }
     }
 
+    // Type inference does not understand that [name] is now always a non-null
+    // String. (There is some imprecision in the negation of the disjunction.)
+    name = JS('String', '#', name);
+
     // TODO(kasperl): If the namer gave us a fresh global name, we may
     // want to remove the numeric suffix that makes it unique too.
     if (name.length > 1 && identical(name.codeUnitAt(0), DOLLAR_CHAR_VALUE)) {