Reapply "Enable full type-checks in checked mode."

sdk/lib/_internal/compiler/implementation/js_backend/backend.dart

Index: sdk/lib/_internal/compiler/implementation/js_backend/backend.dart
diff --git a/sdk/lib/_internal/compiler/implementation/js_backend/backend.dart b/sdk/lib/_internal/compiler/implementation/js_backend/backend.dart
index c3052f44edd40502cd36be7be004cfadd33bb2ea..36bdbc2e74b25c6419370190100e00cbcbbf6d80 100644
--- a/sdk/lib/_internal/compiler/implementation/js_backend/backend.dart
+++ b/sdk/lib/_internal/compiler/implementation/js_backend/backend.dart
@@ -1229,19 +1229,26 @@ class JavaScriptBackend extends Backend {
   void registerIsCheck(DartType type, Enqueuer world, TreeElements elements) {
     world.registerInstantiatedClass(compiler.boolClass, elements);
     bool isTypeVariable = type.kind == TypeKind.TYPE_VARIABLE;
+    bool inCheckedMode = compiler.enableTypeAssertions;
     if (!type.isRaw || isTypeVariable) {
       enqueueInResolution(getSetRuntimeTypeInfo(), elements);
       enqueueInResolution(getGetRuntimeTypeInfo(), elements);
       enqueueInResolution(getGetRuntimeTypeArgument(), elements);
+      if (inCheckedMode) {
+        enqueueInResolution(getAssertSubtype(), elements);
+      }
       enqueueInResolution(getCheckSubtype(), elements);
       if (isTypeVariable) {
-        enqueueInResolution(getGetObjectIsSubtype(), elements);
+        enqueueInResolution(getCheckSubtypeOfRuntimeType(), elements);
+        if (inCheckedMode) {
+          enqueueInResolution(getAssertSubtypeOfRuntimeType(), elements);
+        }
       }
       world.registerInstantiatedClass(compiler.listClass, elements);
     }
     // [registerIsCheck] is also called for checked mode checks, so we
     // need to register checked mode helpers.
-    if (compiler.enableTypeAssertions) {
+    if (inCheckedMode) {
       Element e = getCheckedModeHelper(type, typeCast: false);
       if (e != null) world.addToWorkList(e);
       // We also need the native variant of the check (for DOM types).
@@ -1327,8 +1334,8 @@ class JavaScriptBackend extends Backend {
   }
 
   bool needsRti(ClassElement cls) {
-    return rti.classesNeedingRti.contains(cls.declaration)
-        || compiler.enabledRuntimeType;
+    return rti.classesNeedingRti.contains(cls.declaration) ||
+        compiler.enabledRuntimeType;
   }
 
   bool isDefaultNoSuchMethodImplementation(Element element) {
@@ -1593,8 +1600,9 @@ class JavaScriptBackend extends Backend {
    * backend with implementation types (JSInt, JSString, ...).
    */
   Element getCheckedModeHelper(DartType type, {bool typeCast}) {
-    return compiler.findHelper(getCheckedModeHelperName(
-        type, typeCast: typeCast, nativeCheckOnly: false));
+    SourceString name = getCheckedModeHelperName(
+        type, typeCast: typeCast, nativeCheckOnly: false);
+    return compiler.findHelper(name);
   }
 
   /**
@@ -1693,13 +1701,22 @@ class JavaScriptBackend extends Backend {
         }
       } else {
         if (nativeCheck) {
+          // TODO(karlklose): can we get rid of this branch when we use
+          // interceptors?
           return typeCast
               ? const SourceString("interceptedTypeCast")
               : const SourceString('interceptedTypeCheck');
         } else {
-          return typeCast
-              ? const SourceString("propertyTypeCast")
-              : const SourceString('propertyTypeCheck');
+          if (typeCast) {
+            return const SourceString("propertyTypeCast");
+          }
+          if (type.kind == TypeKind.INTERFACE && !type.isRaw) {
+            return const SourceString('assertSubtype');
+          } else if (type.kind == TypeKind.TYPE_VARIABLE) {
+            return const SourceString('assertSubtypeOfRuntimeType');
+          } else {
+            return const SourceString('propertyTypeCheck');
+          }
         }
       }
     }
@@ -1782,8 +1799,17 @@ class JavaScriptBackend extends Backend {
     return compiler.findHelper(const SourceString('checkSubtype'));
   }
 
-  Element getGetObjectIsSubtype() {
-    return compiler.findHelper(const SourceString('objectIsSubtype'));
+  Element getAssertSubtype() {
+    return compiler.findHelper(const SourceString('assertSubtype'));
+  }
+
+  Element getCheckSubtypeOfRuntimeType() {
+    return compiler.findHelper(const SourceString('checkSubtypeOfRuntimeType'));
+  }
+
+  Element getAssertSubtypeOfRuntimeType() {
+    return compiler.findHelper(
+        const SourceString('assertSubtypeOfRuntimeType'));
   }
 
   Element getThrowNoSuchMethod() {