Introduce OpenWorld.

pkg/compiler/lib/src/ssa/builder.dart

Index: pkg/compiler/lib/src/ssa/builder.dart
diff --git a/pkg/compiler/lib/src/ssa/builder.dart b/pkg/compiler/lib/src/ssa/builder.dart
index 6b69d4b7d7665f7a779d5f1092591bdfd516e65f..bf008a2c8506abdd389af5c5a701b6c0c935968e 100644
--- a/pkg/compiler/lib/src/ssa/builder.dart
+++ b/pkg/compiler/lib/src/ssa/builder.dart
@@ -556,7 +556,7 @@ class SsaBuilder extends ast.Visitor
    */
   List<HInstruction> completeDynamicSendArgumentsList(Selector selector,
       FunctionElement function, List<HInstruction> providedArguments) {
-    assert(selector.applies(function, compiler.closedWorld));
+    assert(selector.applies(function, backend));
     FunctionSignature signature = function.functionSignature;
     List<HInstruction> compiledArguments = new List<HInstruction>(
         signature.parameterCount + 1); // Plus one for receiver.
@@ -650,7 +650,7 @@ class SsaBuilder extends ast.Visitor
               element.isGenerativeConstructorBody,
           message: "Missing selector for inlining of $element."));
       if (selector != null) {
-        if (!selector.applies(function, compiler.closedWorld)) return false;
+        if (!selector.applies(function, backend)) return false;
         if (mask != null &&
             !mask.canHit(function, selector, compiler.closedWorld)) {
           return false;
@@ -3692,8 +3692,7 @@ class SsaBuilder extends ast.Visitor
     // TODO(5347): Try to avoid the need for calling [implementation] before
     // calling [makeStaticArgumentList].
     Selector selector = elements.getSelector(node);
-    assert(invariant(
-        node, selector.applies(function.implementation, compiler.closedWorld),
+    assert(invariant(node, selector.applies(function.implementation, backend),
         message: "$selector does not apply to ${function.implementation}"));
     List<HInstruction> inputs = makeStaticArgumentList(
         selector.callStructure, node.arguments, function.implementation);
@@ -4946,7 +4945,7 @@ class SsaBuilder extends ast.Visitor
     void generateSuperSendSet() {
       Selector setterSelector = elements.getSelector(node);
       if (Elements.isUnresolved(element) ||
-          !setterSelector.applies(element, compiler.closedWorld)) {
+          !setterSelector.applies(element, compiler.backend)) {
         generateSuperNoSuchMethodSend(node, setterSelector, setterInputs);
         pop();
       } else {