dart2js: move native boilerplate code into a separate file.

pkg/compiler/lib/src/js_emitter/native_generator.dart

+// Copyright (c) 2014, 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;
+
+class NativeGenerator {
+  final Function generateEmbeddedGlobalAccess;
+
+  NativeGenerator(this.generateEmbeddedGlobalAccess);
+
+  /**
+   * Emits code that sets the `isolateTag embedded global to a unique string.
+   */
+  jsAst.Expression generateIsolateAffinityTagInitialization() {
+    jsAst.Expression getIsolateTagAccess =
+        generateEmbeddedGlobalAccess(embeddedNames.GET_ISOLATE_TAG);
+    jsAst.Expression isolateTagAccess =
+        generateEmbeddedGlobalAccess(embeddedNames.ISOLATE_TAG);
+
+    return js('''
+      !function() {
+        // On V8, the 'intern' function converts a string to a symbol, which
+        // makes property access much faster.
+        function intern(s) {
+          var o = {};
+          o[s] = 1;
+          return Object.keys(convertToFastObject(o))[0];
+        }
+
+        #getIsolateTag = function(name) {
+          return intern("___dart_" + name + #isolateTag);
+        };
+
+        // 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.
+        var tableProperty = "___dart_isolate_tags_";
+        var usedProperties = Object[tableProperty] ||
+            (Object[tableProperty] = Object.create(null));
+
+        var rootProperty = "_${generateIsolateTagRoot()}";
+        for (var i = 0; ; i++) {
+          var property = intern(rootProperty + "_" + i + "_");
+          if (!(property in usedProperties)) {
+            usedProperties[property] = 1;
+            #isolateTag = property;
+            break;
+          }
+        }
+      }()
+    ''',
+    {'getIsolateTag': getIsolateTagAccess, 'isolateTag': isolateTagAccess});
+  }
+
+  jsAst.Expression generateDispatchPropertyNameInitialization() {
+    jsAst.Expression dispatchPropertyNameAccess =
+        generateEmbeddedGlobalAccess(embeddedNames.DISPATCH_PROPERTY_NAME);
+    jsAst.Expression getIsolateTagAccess =
+        generateEmbeddedGlobalAccess(embeddedNames.GET_ISOLATE_TAG);
+    return js('# = #("dispatch_record")',
+        [dispatchPropertyNameAccess,
+         getIsolateTagAccess]);
+  }
+
+  String generateIsolateTagRoot() {
+    // TODO(sra): MD5 of contributing source code or URIs?
+    return 'ZxYxX';
+  }
+}