Fix bug where constants were not correctly canonicalized.

lib/compiler/implementation/emitter.dart

Index: lib/compiler/implementation/emitter.dart
diff --git a/lib/compiler/implementation/emitter.dart b/lib/compiler/implementation/emitter.dart
index c7fb5b0ee3bd5c4090cab188afa99a368d746fd6..422e3e9a80c78b08d0d3b139ba4e0dcdd5035d74 100644
--- a/lib/compiler/implementation/emitter.dart
+++ b/lib/compiler/implementation/emitter.dart
@@ -147,8 +147,9 @@ function(child, parent) {
               // down to the native method.
               indexOfLastOptionalArgumentInParameters = count;
             }
-            argumentsBuffer[count] =
-                handler.writeJsCode(new StringBuffer(), value).toString();
+            StringBuffer argumentBuffer = new StringBuffer();
+            handler.writeConstant(argumentBuffer, value);
+            argumentsBuffer[count] = argumentBuffer.toString();
           }
         }
       }