Cleanup the namer, and add a test with fields that used to clash with internal names used by the co…

sdk/lib/_internal/compiler/implementation/ssa/builder.dart

Index: sdk/lib/_internal/compiler/implementation/ssa/builder.dart
===================================================================
--- sdk/lib/_internal/compiler/implementation/ssa/builder.dart	(revision 17447)
+++ sdk/lib/_internal/compiler/implementation/ssa/builder.dart	(working copy)
@@ -2997,6 +2997,8 @@
       handleForeignSetCurrentIsolate(node);
     } else if (name == const SourceString('JS_CREATE_ISOLATE')) {
       handleForeignCreateIsolate(node);
+    } else if (name == const SourceString('JS_OPERATOR_IS_PREFIX')) {
+      stack.add(addConstantString(node, backend.namer.operatorIsPrefix()));
     } else {
       throw "Unknown foreign: ${selector}";
     }