Implement PrimitiveOrNull types.

lib/compiler/implementation/ssa/builder.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 class Interceptors {
   Compiler compiler;
   Interceptors(Compiler this.compiler);
 
   SourceString mapOperatorToMethodName(Operator op) {
     String name = op.source.stringValue;
@@ skipping 1030 matching lines @@
                                     Element sourceElement) {
     if (!compiler.enableTypeAssertions) return original;
 
     Type type = sourceElement.computeType(compiler);
     if (type === null) return original;
     if (type.element === compiler.dynamicClass) return original;
     if (type.element === compiler.objectClass) return original;
 
     HType convertedType = new HType.fromBoundedType(type, compiler, true);
 
-    // TODO(ngeoffray): the factory method should never return null.
-    if (convertedType === null) {
-      return original;
-    }
-
     // No need to convert if we know the instruction has
     // [convertedType] as a bound.
     if (original.guaranteedType == convertedType) {
       return original;
     }
 
     HInstruction instruction =
         new HTypeConversion(convertedType, original, true);
     add(instruction);
     return instruction;
@@ skipping 2250 matching lines @@
                                    <HInstruction>[target, input],
                                    HType.STRING));
     return builder.pop();
   }
 
   HInstruction result() {
     flushLiterals();
     return prefix;
   }
 }