implement opassign, fix bugs in pre/postfix, introduce a let* helper

lib/runtime/dart/_isolate_helper.js

Index: lib/runtime/dart/_isolate_helper.js
diff --git a/lib/runtime/dart/_isolate_helper.js b/lib/runtime/dart/_isolate_helper.js
index b74a6dded4ca1da676d28b32ff92dcb3dce04da1..47d887654020d3b12ec5601c0fa55895a0f3a04d 100644
--- a/lib/runtime/dart/_isolate_helper.js
+++ b/lib/runtime/dart/_isolate_helper.js
@@ -358,11 +358,13 @@ var _isolate_helper;
   let _activeJsAsyncCount = Symbol('_activeJsAsyncCount');
   // Function enterJsAsync: () → dynamic
   function enterJsAsync() {
-    exports._globalState.topEventLoop[_activeJsAsyncCount] = dart.notNull(exports._globalState.topEventLoop[_activeJsAsyncCount]) + 1;
+    let o$ = exports._globalState.topEventLoop;
+    o$[_activeJsAsyncCount] = dart.notNull(o$[_activeJsAsyncCount]) + 1;
   }
   // Function leaveJsAsync: () → dynamic
   function leaveJsAsync() {
-    exports._globalState.topEventLoop[_activeJsAsyncCount] = dart.notNull(exports._globalState.topEventLoop[_activeJsAsyncCount]) - 1;
+    let o$ = exports._globalState.topEventLoop;
+    o$[_activeJsAsyncCount] = dart.notNull(o$[_activeJsAsyncCount]) - 1;
     dart.assert(dart.notNull(exports._globalState.topEventLoop[_activeJsAsyncCount]) >= 0);
   }
   // Function isWorker: () → bool
@@ -481,7 +483,12 @@ var _isolate_helper;
   let _close = Symbol('_close');
   class _IsolateContext extends core.Object {
     _IsolateContext() {
-      this.id = ((x$) => exports._globalState.nextIsolateId = dart.notNull(x$) + 1, x$)(exports._globalState.nextIsolateId);
+      this.id = ((o$, x$) => {
+        o$ = exports._globalState;
+        x$ = o$.nextIsolateId;
+        o$.nextIsolateId = dart.notNull(x$) + 1;
+        return x$;
+      })();
       this.ports = new (core.Map$(core.int, RawReceivePortImpl))();
       this.weakPorts = new (core.Set$(core.int))();
       this.isolateStatics = _foreign_helper.JS_CREATE_ISOLATE();
@@ -1005,8 +1012,9 @@ var _isolate_helper;
       return IsolateNatives.spawn(null, uri.toString(), args, message, isLight, isSpawnUri, startPaused);
     }
     static spawn(functionName, uri, args, message, isLight, isSpawnUri, startPaused) {
-      if (dart.notNull(uri != null) && dart.notNull(uri.endsWith(".dart")))
-        uri = ".js";
+      if (dart.notNull(uri != null) && dart.notNull(uri.endsWith(".dart"))) {
+        uri = core.String['+'](uri, ".js");
+      }
       let port = new isolate.ReceivePort();
       let completer = dart.as(new async.Completer(), async.Completer$(core.List));
       port.first.then((msg) => {
@@ -1091,7 +1099,9 @@ var _isolate_helper;
         };
       }(_foreign_helper.DART_CLOSURE_TO_JS(IsolateNatives[_processWorkerMessage]), worker);
       worker.onmessage = processWorkerMessageTrampoline;
-      let workerId = ((x$) => exports._globalState.nextManagerId = dart.notNull(x$) + 1, x$)(exports._globalState.nextManagerId);
+      let o$ = exports._globalState;
+      let workerId = o$.nextManagerId;
+      o$.nextManagerId = dart.notNull(workerId) + 1;
       IsolateNatives.workerIds.set(worker, workerId);
       exports._globalState.managers.set(workerId, worker);
       worker.postMessage(_serializeMessage(dart.map({command: 'start', id: workerId, replyTo: _serializeMessage(replyPort), args: args, msg: _serializeMessage(message), isSpawnUri: isSpawnUri, startPaused: startPaused, functionName: functionName})));
@@ -1192,13 +1202,13 @@ var _isolate_helper;
   class RawReceivePortImpl extends core.Object {
     RawReceivePortImpl(handler) {
       this[_handler] = handler;
-      this[_id] = ((x$) => RawReceivePortImpl[_nextFreeId] = dart.notNull(x$) + 1, x$)(RawReceivePortImpl[_nextFreeId]);
+      this[_id] = ((x$) => (x$ = RawReceivePortImpl[_nextFreeId], RawReceivePortImpl[_nextFreeId] = dart.notNull(x$) + 1, x$))();
       this[_isClosed] = false;
       exports._globalState.currentContext.register(this[_id], this);
     }
     weak(handler) {
       this[_handler] = handler;
-      this[_id] = ((x$) => RawReceivePortImpl[_nextFreeId] = dart.notNull(x$) + 1, x$)(RawReceivePortImpl[_nextFreeId]);
+      this[_id] = ((x$) => (x$ = RawReceivePortImpl[_nextFreeId], RawReceivePortImpl[_nextFreeId] = dart.notNull(x$) + 1, x$))();
       this[_isClosed] = false;
       exports._globalState.currentContext.registerWeak(this[_id], this);
     }
@@ -1352,11 +1362,11 @@ var _isolate_helper;
       let hash = this[_id];
       hash = dart.notNull(hash) >> 0 ^ (dart.notNull(hash) / 4294967296).truncate();
       hash = ~dart.notNull(hash) + (dart.notNull(hash) << 15) & 4294967295;
-      hash = dart.notNull(hash) >> 12;
+      hash = dart.notNull(hash) ^ dart.notNull(hash) >> 12;
       hash = dart.notNull(hash) * 5 & 4294967295;
-      hash = dart.notNull(hash) >> 4;
+      hash = dart.notNull(hash) ^ dart.notNull(hash) >> 4;
       hash = dart.notNull(hash) * 2057 & 4294967295;
-      hash = dart.notNull(hash) >> 16;
+      hash = dart.notNull(hash) ^ dart.notNull(hash) >> 16;
       return hash;
     }
     ['=='](other) {