Add extra tracing to Debug_InterruptIsolate test.

runtime/vm/dart.h

 // Copyright (c) 2011, 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_DART_H_
 #define VM_DART_H_
 
 #include "include/dart_api.h"
 #include "vm/allocation.h"
 
@@ skipping 25 matching lines @@
   static Isolate* CreateIsolate(const char* name_prefix,
                                 const Dart_IsolateFlags& api_flags);
   static RawError* InitializeIsolate(const uint8_t* snapshot, void* data);
   static void RunShutdownCallback();
   static void ShutdownIsolate(Isolate* isolate);
   static void ShutdownIsolate();
 
   static Isolate* vm_isolate() { return vm_isolate_; }
   static ThreadPool* thread_pool() { return thread_pool_; }
 
+  // Returns a timestamp for use in debugging output in milliseconds
+  // since start time.
+  static int64_t timestamp();
+
   static void set_pprof_symbol_generator(DebugInfo* value) {
     pprof_symbol_generator_ = value;
   }
   static DebugInfo* pprof_symbol_generator() { return pprof_symbol_generator_; }
 
   static LocalHandle* AllocateReadOnlyApiHandle();
   static bool IsReadOnlyApiHandle(Dart_Handle handle);
 
   static uword AllocateReadOnlyHandle();
   static bool IsReadOnlyHandle(uword address);
 
   static const uint8_t* instructions_snapshot_buffer() {
     return instructions_snapshot_buffer_;
   }
   static void set_instructions_snapshot_buffer(const uint8_t* buffer) {
     instructions_snapshot_buffer_ = buffer;
   }
   static bool IsRunningPrecompiledCode() {
     return instructions_snapshot_buffer_ != NULL;
   }
 
  private:
   static void WaitForIsolateShutdown();
 
   static Isolate* vm_isolate_;
+  static int64_t start_time_;
   static ThreadPool* thread_pool_;
   static DebugInfo* pprof_symbol_generator_;
   static ReadOnlyHandles* predefined_handles_;
   static const uint8_t* instructions_snapshot_buffer_;
 };
 
 }  // namespace dart
 
 #endif  // VM_DART_H_