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

Index: pkg/compiler/lib/src/js_emitter/old_emitter/emitter.dart
diff --git a/pkg/compiler/lib/src/js_emitter/old_emitter/emitter.dart b/pkg/compiler/lib/src/js_emitter/old_emitter/emitter.dart
index 95ea5d973d6a6062230a42196ffc443c6c052dfd..88095ba3e09c7255defc0b98fbb785c5931cd548 100644
--- a/pkg/compiler/lib/src/js_emitter/old_emitter/emitter.dart
+++ b/pkg/compiler/lib/src/js_emitter/old_emitter/emitter.dart
@@ -1413,10 +1413,16 @@ class OldEmitter implements Emitter {
       /// 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 literal that V8 shouldn not try to optimize with a

[ahe, 2015/01/07 12:20:16]

shouldn't (remove "not").

map doesn't return an "object literal", just an "object".

[zarah, 2015/01/07 13:45:17]

Done.

+// 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}

[ahe, 2015/01/07 12:20:16]

Now that this is parsed, I suggest you reformat it: one statement per line.

[zarah, 2015/01/07 13:45:17]

Done.

+''');
+    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
@@ -1427,7 +1433,7 @@ class OldEmitter implements Emitter {
       if(isProgramSplit) {
         mainBuffer.write('${globalsHolder}.$globalObject$_=${_}');
       }
-      mainBuffer.write('new dart$N');
+      mainBuffer.write('map()$N');
     }
 
     mainBuffer.write('function ${namer.isolateName}()$_{}\n');
@@ -1477,9 +1483,10 @@ class OldEmitter implements Emitter {
                   compiler))
           ..write(n);
 
-      mainBuffer..write('$parseReflectionDataName([$n')
+      mainBuffer..write('var dart = [$n')
                 ..write(libraryBuffer)
-                ..write('])$N');
+                ..write(']$N')
+                ..write('$parseReflectionDataName(dart)$N');
     }
 
     interceptorEmitter.emitGetInterceptorMethods(mainBuffer);
@@ -1924,9 +1931,10 @@ function(originalDescriptor, name, holder, isStatic, globalFunctionsAccess) {
       // to Isolate.$finishIsolateConstructor.
          outputBuffer
            ..write('var ${namer.currentIsolate}$_=$_$isolatePropertiesName$N')
-           ..write('$parseReflectionDataName([$n')
+           ..write('var dart = [$n ')
            ..addBuffer(libraryDescriptorBuffer)
-           ..write('])$N');
+           ..write(']$N')
+           ..write('$parseReflectionDataName(dart)$N');
 
       }