Also time external callbacks from generated code.

src/assembler.cc

Index: src/assembler.cc
diff --git a/src/assembler.cc b/src/assembler.cc
index 344e203b6da173027c4de1dc5750c4cab9c10dd6..25157be2eb42524c9901b4dbb8050b6cc224bb12 100644
--- a/src/assembler.cc
+++ b/src/assembler.cc
@@ -1056,6 +1056,20 @@ ExternalReference ExternalReference::compute_output_frames_function(
 }
 
 
+ExternalReference ExternalReference::log_enter_external_function(
+    Isolate* isolate) {
+  return ExternalReference(
+      Redirect(isolate, FUNCTION_ADDR(Logger::EnterExternal)));
+}
+
+
+ExternalReference ExternalReference::log_leave_external_function(
+    Isolate* isolate) {
+  return ExternalReference(
+      Redirect(isolate, FUNCTION_ADDR(Logger::LeaveExternal)));
+}
+
+
 ExternalReference ExternalReference::keyed_lookup_cache_keys(Isolate* isolate) {
   return ExternalReference(isolate->keyed_lookup_cache()->keys_address());
 }