Fix DOM Isolate affinity for interceptors

sdk/lib/_internal/compiler/implementation/js_emitter/code_emitter_task.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of dart2js.js_emitter;
 
 /**
  * Generates the code for all used classes in the program. Static fields (even
  * in classes) are ignored, since they can be treated as non-class elements.
  *
@@ skipping 956 matching lines @@
                            Element appMain,
                            Element isolateMain) {
     String mainAccess = "${namer.isolateStaticClosureAccess(appMain)}";
     // Since we pass the closurized version of the main method to
     // the isolate method, we must make sure that it exists.
     return "${namer.isolateAccess(isolateMain)}($mainAccess)";
   }
 
   jsAst.Expression generateDispatchPropertyInitialization() {
     return js('!#', js.fun([], [
-        js('var objectProto = Object.prototype'),
+
+        // On V8, the 'intern' function converts a string to a symbol, which
+        // makes property access much faster.
+        new jsAst.FunctionDeclaration(new jsAst.VariableDeclaration('intern'),
+            js.fun(['s'], [
+                js('var o = {}'),
+                js('o[s] = 1'),
+                js.return_(js('Object.keys(convertToFastObject(o))[0]'))])),
+
+        // To ensure that different programs loaded into the same context (page)
+        // use distinct dispatch properies, we place an object on `Object` to
+        // contain the names already in use.
+        js('var tableProperty = "___dart_dispatch_property_names_"'),
+        js('var usedProperties = Object[tableProperty] ||'
+            '(Object[tableProperty] = Object.create(null))'),

[floitsch, 2014/02/12 15:33:39]

We could also just store the counter of the last used name.

[sra1, 2014/02/12 22:01:20]

Not if every program has an MD5-like root property to make clashes unlikely.

+
+        js('var rootProperty = "${generateDispatchPropertyName(0)}"'),
         js.for_('var i = 0', null, 'i++', [
-            js('var property = "${generateDispatchPropertyName(0)}"'),
-            js.if_('i > 0', js('property = rootProperty + "_" + i')),
-            js.if_('!(property in  objectProto)',
-                   js.return_(
-                       js('init.dispatchPropertyName = property')))])])());
+            js('property = intern(rootProperty + "_" + i + "_")'),

[floitsch, 2014/02/12 10:38:25]

Isn't generateDispatchPropertyName supposed to do that?
Otherwise, why does it have a seed?

[sra1, 2014/02/12 22:01:20]

The seed was for when I was generating a list of names.

There used to be a getter function created with 'new Function'.  The CSP version
had a list of explicit functions generated with different seeds at compile-time.
The MD5 root would mean in practice that the clashes only happen for multiple
instances of the same program, requiring a less deep stack of explicit
functions.

I'm removing the seed at this point.
It might get added back switch back to using a compiled getter using direct
property syntax instead of a "a[b]".

+            js.if_('!(property in usedProperties)', [
+                js('usedProperties[property] = 1'),

[floitsch, 2014/02/12 10:38:25]

That line seems to be important :)

+                js.return_(
+                    js('init.dispatchPropertyName = property'))])])])());
   }
 
   String generateDispatchPropertyName(int seed) {
     // TODO(sra): MD5 of contributing source code or URIs?
     return '___dart_dispatch_record_ZxYxX_${seed}_';
   }
 
   emitMain(CodeBuffer buffer) {
     if (compiler.isMockCompilation) return;
     Element main = compiler.mainFunction;
@@ skipping 608 matching lines @@
     String sourceMap = buildSourceMap(mainBuffer, compiledFile);
     compiler.outputProvider(name, 'js.map')
         ..add(sourceMap)
         ..close();
   }
 
   void registerReadTypeVariable(TypeVariableElement element) {
     readTypeVariables.add(element);
   }
 }