Improve timeline iterators and tests

runtime/vm/timeline.h

 // Copyright (c) 2015, 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.
 
 #ifndef VM_TIMELINE_H_
 #define VM_TIMELINE_H_
 
 #include "vm/allocation.h"
 #include "vm/bitfield.h"
 
@@ skipping 73 matching lines @@
   int64_t TimeOrigin() const;
   int64_t AsyncId() const;
   int64_t TimeDuration() const;
 
   void PrintJSON(JSONStream* stream) const;
 
   ThreadId thread() const {
     return thread_;
   }
 
+  const char* label() const {
+    return label_;
+  }
+
  private:
   struct TimelineEventArgument {
     const char* name;
     char* value;
   };
 
   int64_t timestamp0_;
   int64_t timestamp1_;
   TimelineEventArgument* arguments_;
   intptr_t arguments_length_;
@@ skipping 364 matching lines @@
   intptr_t block_index_;
 };
 
 
 // An iterator for blocks.
 class TimelineEventBlockIterator {
  public:
   explicit TimelineEventBlockIterator(TimelineEventRecorder* recorder);
   ~TimelineEventBlockIterator();
 
-  void Reset();
-  bool Next();
+  void Reset(TimelineEventRecorder* recorder);
 
-  TimelineEventBlock* current() const {
-    return current_;
-  }
+  // Returns false when there are no more blocks.
+  bool HasNext() const;
+
+  // Returns the next block and moves forward.
+  TimelineEventBlock* Next();
 
  private:
   TimelineEventBlock* current_;
   TimelineEventRecorder* recorder_;
 };
 
 }  // namespace dart
 
 #endif  // VM_TIMELINE_H_