Add support to trace warnings in TraceBuffer.

runtime/vm/trace_buffer_test.cc

Index: runtime/vm/trace_buffer_test.cc
===================================================================
--- runtime/vm/trace_buffer_test.cc	(revision 37244)
+++ runtime/vm/trace_buffer_test.cc	(working copy)
@@ -104,4 +104,51 @@
 }
 
 
+TEST_CASE(TraceBufferTraceWarning) {
+  Isolate* isolate = Isolate::Current();
+  TraceBuffer::Init(isolate, 3);
+  TraceBuffer* trace_buffer = isolate->trace_buffer();
+  const String& url = String::Handle(isolate, String::New("Plug"));
+  const String& source = String::Handle(isolate, String::New("240V"));
+  const Script& script = Script::Handle(isolate,
+      Script::New(url, source, RawScript::kScriptTag));
+  {
+    const intptr_t token_pos = 0;
+    const char* message = "High Voltage";
+    TraceBuffer::TraceWarningF(isolate, script, token_pos, "%s", message);
+    {
+      JSONStream js;
+      trace_buffer->PrintToJSONStream(&js);
+      EXPECT_SUBSTRING("{\"type\":\"TraceBuffer\",\"members\":["
+                       "{\"type\":\"TraceBufferEntry\",\"time\":",
+                       js.ToCString());
+      // Skip time.
+      EXPECT_SUBSTRING("\"message\":{\"type\":\"Warning\","
+                       "\"script\":{\"type\":\"@Script\",\"id\":"
+                       "\"scripts\\/Plug\",\"name\":\"Plug\",\"user_name\":"
+                       "\"Plug\",\"kind\":\"script\"},\"tokenPos\":0,"
+                       "\"message\":\"High Voltage\"}}]}",
+                       js.ToCString());
+    }
+  }
+  {
+    const intptr_t token_pos = 1;
+    const char* message = "Low Voltage";
+    TraceBuffer::TraceWarningF(isolate, script, token_pos, "%s", message);
+  }
+  EXPECT_EQ(2, trace_buffer->Length());
+  EXPECT_STREQ("{\"type\":\"Warning\",\"script\":{\"type\":\"@Script\",\"id\":"
+               "\"scripts\\/Plug\",\"name\":\"Plug\",\"user_name\":\"Plug\","
+               "\"kind\":\"script\"},\"tokenPos\":0,\"message\":"
+               "\"High Voltage\"}",
+               trace_buffer->At(0)->message);
+  EXPECT_STREQ("{\"type\":\"Warning\",\"script\":{\"type\":\"@Script\",\"id\":"
+               "\"scripts\\/Plug\",\"name\":\"Plug\",\"user_name\":\"Plug\","
+               "\"kind\":\"script\"},\"tokenPos\":1,\"message\":"
+               "\"Low Voltage\"}",
+               trace_buffer->At(1)->message);
+
+  delete trace_buffer;
+}
+
 }  // namespace dart