refactor emitMemberName to be used more consistently

test/codegen/expect/opassign.js

 var opassign;
 (function(exports) {
   'use strict';
   dart.copyProperties(exports, {
     get index() {
       core.print('called "index" getter');
       return 0;
     }
   });
   dart.defineLazyProperties(exports, {
@@ skipping 10 matching lines @@
   class Foo extends core.Object {
     Foo() {
       this.x = 100;
     }
   }
   // Function main: () → dynamic
   function main() {
     let f = dart.map([0, 40]);
     core.print('should only call "index" 2 times:');
     let i = exports.index;
-    f.set(i, dart.dbinary(f.get(i), '+', 1));
+    f.set(i, dart.dsend(f.get(i), '+', 1));
     forcePostfix((() => {
       let i = exports.index, x$ = f.get(i);
-      f.set(i, dart.dbinary(x$, '+', 1));
+      f.set(i, dart.dsend(x$, '+', 1));
       return x$;
     })());
     core.print('should only call "foo" 2 times:');
     let o = exports.foo;
-    dart.dput(o, 'x', dart.dbinary(dart.dload(o, 'x'), '+', 1));
+    dart.dput(o, 'x', dart.dsend(dart.dload(o, 'x'), '+', 1));
     forcePostfix((() => {
       let o = exports.foo, x$ = dart.dload(o, 'x');
-      dart.dput(o, 'x', dart.dbinary(x$, '+', 1));
+      dart.dput(o, 'x', dart.dsend(x$, '+', 1));
       return x$;
     })());
     core.print('op assign test, should only call "index" twice:');
     let i = exports.index;
-    f.set(i, dart.dbinary(f.get(i), '+', f.get(exports.index)));
+    f.set(i, dart.dsend(f.get(i), '+', f.get(exports.index)));
   }
   // Function forcePostfix: (dynamic) → dynamic
   function forcePostfix(x) {
   }
   // Exports:
   exports.Foo = Foo;
   exports.main = main;
   exports.forcePostfix = forcePostfix;
 })(opassign || (opassign = {}));