Add API to set thread name

runtime/vm/os_thread.cc

Index: runtime/vm/os_thread.cc
diff --git a/runtime/vm/os_thread.cc b/runtime/vm/os_thread.cc
index b381692c08fc8b889c30ac0a4970d85170ba18a2..947b7f6955f318d3eef1b39aec80ad2285a38e4f 100644
--- a/runtime/vm/os_thread.cc
+++ b/runtime/vm/os_thread.cc
@@ -63,6 +63,18 @@ OSThread::~OSThread() {
 }
 
 
+
+void OSThread::SetName(const char* name) {
+  MutexLocker ml(thread_list_lock_);
+  // Clear the old thread name.
+  if (name_ != NULL) {
+    free(name_);
+    name_ = NULL;
+  }
+  set_name(name);
+}
+
+
 void OSThread::DisableThreadInterrupts() {
   ASSERT(OSThread::Current() == this);
   AtomicOperations::FetchAndIncrement(&thread_interrupt_disabled_);