Added API Dart_PostCMessage for posting a Dart_CMessage structure

runtime/bin/dartutils.cc

Index: runtime/bin/dartutils.cc
diff --git a/runtime/bin/dartutils.cc b/runtime/bin/dartutils.cc
index 962748aec3bda762e6135ae4bf01e66c8c08024e..6ac5079047f81f700aefeb2ae4ac83465b80db96 100644
--- a/runtime/bin/dartutils.cc
+++ b/runtime/bin/dartutils.cc
@@ -5,6 +5,7 @@
 #include "bin/dartutils.h"
 
 #include "bin/file.h"
+#include "include/dart_api.h"
 #include "platform/assert.h"
 #include "platform/globals.h"
 
@@ -229,3 +230,23 @@ const char* DartUtils::GetCanonicalPath(const char* reference_dir,
   free(absolute_filename);
   return canonical_filename;
 }
+
+
+bool DartUtils::PostNull(Dart_Port port_id) {
+  // Post a message with just the null object.
+  Dart_CObject object;
+  object.type = Dart_CObject::kNull;
+  return Dart_PostCObject(port_id, &object);
+}
+
+
+bool DartUtils::PostInt32(Dart_Port port_id, int32_t value) {
+  // Post a message with the integer value.
+  int32_t min = 0xc0000000;  // -1073741824
+  int32_t max = 0x3fffffff;  // 1073741823
+  ASSERT(min <= value && value < max);
+  Dart_CObject object;
+  object.type = Dart_CObject::kInt32;
+  object.value.as_int32 = value;
+  return Dart_PostCObject(port_id, &object);
+}