dart2js: change output so that in stack traces, dart method names get prefixed with 'dart.' instead…

pkg/compiler/lib/src/js_emitter/old_emitter/emitter.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 OldEmitter implements Emitter {
   final Compiler compiler;
   final CodeEmitterTask task;
@@ skipping 1395 matching lines @@
 }""",
           { 'helper': js('this.#', [namer.incrementalHelperName]),
             'schemaChange': buildSchemaChangeFunction(),
             'addMethod': buildIncrementalAddMethod() }), compiler));
     }
     if (isProgramSplit) {
       /// We collect all the global state of the, so it can be passed to the
       /// initializer of deferred files.
       mainBuffer.write('var ${globalsHolder}$_=${_}Object.create(null)$N');
     }
-    mainBuffer.write('function dart()$_{$n'
-        '${_}${_}this.x$_=${_}0$N'
-        '${_}${_}delete this.x$N'
-        '}$n');
+
+    jsAst.Statement mapFunction = js.statement('''
+// [map] returns an object that V8 shouldn't try to optimize with a hidden
+// class. This prevents a potential performance problem where V8 tries to build
+// a hidden class for an object used as a hashMap.
+// It requires fewer characters to declare a variable as a parameter than
+// with `var`.
+  function map(x) {
+    x = Object.create(null);
+    x.x = 0;
+    delete x.x;
+    return x;
+  }
+''');
+    mainBuffer.write(jsAst.prettyPrint(mapFunction, compiler));
     for (String globalObject in Namer.reservedGlobalObjectNames) {
       // The global objects start as so-called "slow objects". For V8, this
       // means that it won't try to make map transitions as we add properties
       // to these objects. Later on, we attempt to turn these objects into
       // fast objects by calling "convertToFastObject" (see
       // [emitConvertToFastObjectFunction]).
       mainBuffer.write('var ${globalObject}$_=${_}');
       if(isProgramSplit) {
         mainBuffer.write('${globalsHolder}.$globalObject$_=${_}');
       }
-      mainBuffer.write('new dart$N');
+      mainBuffer.write('map()$N');
     }
 
     mainBuffer.write('function ${namer.isolateName}()$_{}\n');
     if (isProgramSplit) {
       mainBuffer.write(
           '${globalsHolder}.${namer.isolateName}$_=$_${namer.isolateName}$N'
           '${globalsHolder}.$initName$_=${_}$initName$N'
           '${globalsHolder}.$parseReflectionDataName$_=$_'
             '$parseReflectionDataName$N');
     }
@@ skipping 29 matching lines @@
         elementDescriptors.remove(library);
       }
 
       mainBuffer
           ..write(
               jsAst.prettyPrint(
                   getReflectionDataParser(this, backend),
                   compiler))
           ..write(n);
 
-      mainBuffer..write('$parseReflectionDataName([$n')
+      // The argument to reflectionDataParser is assigned to a temporary 'dart'
+      // so that 'dart.' will appear as the prefix to dart methods in stack
+      // traces and profile entries.

[ahe, 2015/01/07 14:19:11]

(on V8).

+      mainBuffer..write('var dart = [$n')
                 ..write(libraryBuffer)
-                ..write('])$N');
+                ..write(']$N')
+                ..write('$parseReflectionDataName(dart)$N');
     }
 
     interceptorEmitter.emitGetInterceptorMethods(mainBuffer);
     interceptorEmitter.emitOneShotInterceptors(mainBuffer);
 
     if (task.outputContainsConstantList) {
       emitMakeConstantList(mainBuffer);
     }
 
     // Constants in checked mode call into RTI code to set type information
@@ skipping 424 matching lines @@
                     '$globalsHolder.$parseReflectionDataName$N')
           ..write('var ${namer.isolateName}$_=$_'
                     '${globalsHolder}.${namer.isolateName}$N');
       if (libraryDescriptorBuffer != null) {
       // TODO(ahe): This defines a lot of properties on the
       // Isolate.prototype object.  We know this will turn it into a
       // slow object in V8, so instead we should do something similar
       // to Isolate.$finishIsolateConstructor.
          outputBuffer
            ..write('var ${namer.currentIsolate}$_=$_$isolatePropertiesName$N')
-           ..write('$parseReflectionDataName([$n')
+            // The argument to reflectionDataParser is assigned to a temporary
+            // 'dart' so that 'dart.' will appear as the prefix to dart methods
+            // in stack traces and profile entries.

[ahe, 2015/01/07 14:19:11]

Refactor code so you don't need to duplicate the comment.

+           ..write('var dart = [$n ')
            ..addBuffer(libraryDescriptorBuffer)
-           ..write('])$N');
+           ..write(']$N')
+           ..write('$parseReflectionDataName(dart)$N');
 
       }
 
       // Set the currentIsolate variable to the current isolate (which is
       // provided as second argument).
       // We need to do this, because we use the same variable for setting up
       // the isolate-properties and for storing the current isolate. During
       // the setup (the code above this lines) we must set the variable to
       // the isolate-properties.
       // After we have done the setup it must point to the current Isolate.
@@ skipping 88 matching lines @@
     for (Element element in compiler.enqueuer.codegen.newlyEnqueuedElements) {
       if (element.isInstanceMember) {
         cachedClassBuilders.remove(element.enclosingClass);
 
         nativeEmitter.cachedBuilders.remove(element.enclosingClass);
 
       }
     }
   }
 }