Add support to trace warnings in TraceBuffer.

runtime/vm/trace_buffer.h

Index: runtime/vm/trace_buffer.h
===================================================================
--- runtime/vm/trace_buffer.h	(revision 37220)
+++ runtime/vm/trace_buffer.h	(working copy)
@@ -12,6 +12,7 @@
 namespace dart {
 
 class JSONStream;
+class Script;
 
 struct TraceBufferEntry {
   int64_t micros;
@@ -37,6 +38,15 @@
   void Trace(const char* message);
   void TraceF(const char* format, ...) PRINTF_ATTRIBUTE(2, 3);
 
+  // TODO(regis): Make these methods if we decide to allocate a trace buffer
+  // by default in each isolate.
+  static void TraceWarningF(Isolate* isolate,
+                            const Script& script, intptr_t token_pos,
+                            const char* format, ...) PRINTF_ATTRIBUTE(4, 5);
+  static void TraceWarningV(Isolate* isolate,
+                            const Script& script, intptr_t token_pos,
+                            const char* format, va_list args);
+
   void PrintToJSONStream(JSONStream* stream) const;
 
  private: