Support configuring DDC runtime settings before the application starts and normalize API for config…

pkg/dev_compiler/tool/input_sdk/private/ddc_runtime/profile.dart

 // Copyright (c) 2017, 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.
 
 /// This file supports profiling dynamic calls.
 part of dart._runtime;
 
 class _MethodStats {
   final String typeName;
   final String frame;
@@ skipping 96 matching lines @@
     var stats = callMethodStats[key];
     ret.add([stats.typeName, stats.frame, stats.count.round()]);
   }
   return ret;
 }
 
 clearDynamicStats() {
   _callMethodRecords.clear();
 }
 
-bool trackProfile = JS('bool', 'dart.global.trackDdcProfile');
+bool _trackProfile = false;
+
+void trackProfile(bool flag) {
+  _trackProfile = flag;
+}
 
 _trackCall(obj) {
   if (JS('bool', '!#', trackProfile)) return;
   int index = -1;
   _totalCallRecords++;
   if (_callMethodRecords.length == _callRecordSampleSize) {
     // Ensure that each sample has an equal
     // _callRecordSampleSize / _totalCallRecords chance of inclusion
     // by choosing to include the new record in the sample the with the
     // appropriate probability randomly evicting one of the existing records.
     // Unfortunately we can't use the excellent Random.nextInt method defined
     // by Dart from within this library.
     index = JS('int', 'Math.floor(Math.random() * #)', _totalCallRecords);
     if (index >= _callMethodRecords.length) return; // don't sample
   }
   var record =
       new _CallMethodRecord(JS('', 'new Error()'), getReifiedType(obj));
   if (index == -1) {
     _callMethodRecords.add(record);
   } else {
     _callMethodRecords[index] = record;
   }
 }