Fix bug with namer: use the same encoding for an instance method, whether it is an invocation or a …

sdk/lib/_internal/compiler/implementation/js_backend/namer.dart

Index: sdk/lib/_internal/compiler/implementation/js_backend/namer.dart
===================================================================
--- sdk/lib/_internal/compiler/implementation/js_backend/namer.dart	(revision 21721)
+++ sdk/lib/_internal/compiler/implementation/js_backend/namer.dart	(working copy)
@@ -364,8 +364,7 @@
       assert(name == operatorNameToIdentifier(name));
       StringBuffer buffer = new StringBuffer();
       for (SourceString argumentName in selector.getOrderedNamedArguments()) {
-        buffer.write(r'$');
-        argumentName.printOn(buffer);
+        buffer.write('\$${safeName(argumentName.slowToString())}');
       }
       String suffix = '\$${selector.argumentCount}$buffer';
       // We don't mangle the closure invoking function name because it