Reduce use of Compiler.closedWorld

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

Index: pkg/compiler/lib/src/ssa/graph_builder.dart
diff --git a/pkg/compiler/lib/src/ssa/graph_builder.dart b/pkg/compiler/lib/src/ssa/graph_builder.dart
index e5dce33ba569fc5127dcd44b913485562f372d9d..c35e34fb48e50bcfcb3f7a0d7477c8ea879ae4bf 100644
--- a/pkg/compiler/lib/src/ssa/graph_builder.dart
+++ b/pkg/compiler/lib/src/ssa/graph_builder.dart
@@ -42,6 +42,10 @@ abstract class GraphBuilder {
 
   CodegenRegistry get registry;
 
+  ClosedWorld get closedWorld => compiler.closedWorld;
+
+  CommonMasks get commonMasks => closedWorld.commonMasks;
+
   /// Used to track the locals while building the graph.
   LocalsHandler localsHandler;
 
@@ -75,8 +79,8 @@ abstract class GraphBuilder {
 
   /// Pushes a boolean checking [expression] against null.
   pushCheckNull(HInstruction expression) {
-    push(new HIdentity(
-        expression, graph.addConstantNull(compiler), null, backend.boolType));
+    push(new HIdentity(expression, graph.addConstantNull(compiler), null,
+        closedWorld.commonMasks.boolType));
   }
 
   void dup() {
@@ -225,7 +229,7 @@ abstract class GraphBuilder {
         TypeInfoExpressionKind.INSTANCE,
         (type.element as ClassElement).thisType,
         rtiInputs,
-        backend.dynamicType);
+        closedWorld.commonMasks.dynamicType);
     add(typeInfo);
     return callSetRuntimeTypeInfo(typeInfo, newObject);
   }