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/variable_allocator.dart

Index: sdk/lib/_internal/compiler/implementation/ssa/variable_allocator.dart
===================================================================
--- sdk/lib/_internal/compiler/implementation/ssa/variable_allocator.dart	(revision 17533)
+++ sdk/lib/_internal/compiler/implementation/ssa/variable_allocator.dart	(working copy)
@@ -472,9 +472,10 @@
 
   String allocateWithHint(String originalName) {
     int i = 0;
-    String name = JsNames.getValid(originalName);
+    JavaScriptBackend backend = compiler.backend;
+    String name = backend.namer.safeName(originalName);
     while (usedNames.contains(name)) {
-      name = JsNames.getValid('$originalName${i++}');
+      name = backend.namer.safeName('$originalName${i++}');
     }
     return name;
   }