Add API timeline durations for snapshot creation

runtime/vm/dart_api_impl.cc

Index: runtime/vm/dart_api_impl.cc
diff --git a/runtime/vm/dart_api_impl.cc b/runtime/vm/dart_api_impl.cc
index cb540bc058b449093b21824851a0d9c7f0bf805a..0dc30a6357e89527d1249636cae3faa63420212a 100644
--- a/runtime/vm/dart_api_impl.cc
+++ b/runtime/vm/dart_api_impl.cc
@@ -1466,6 +1466,7 @@ DART_EXPORT Dart_Handle Dart_CreateSnapshot(
     intptr_t* isolate_snapshot_size) {
   ASSERT(FLAG_load_deferred_eagerly);
   DARTSCOPE(Thread::Current());
+  API_TIMELINE_DURATION;
   Isolate* I = T->isolate();
   if (vm_isolate_snapshot_buffer != NULL &&
       vm_isolate_snapshot_size == NULL) {
@@ -1537,6 +1538,7 @@ static Dart_Handle createLibrarySnapshot(Dart_Handle library,
 
 DART_EXPORT Dart_Handle Dart_CreateScriptSnapshot(uint8_t** buffer,
                                                   intptr_t* size) {
+  API_TIMELINE_DURATION;
   return createLibrarySnapshot(Dart_Null(), buffer, size);
 }
 
@@ -1544,6 +1546,7 @@ DART_EXPORT Dart_Handle Dart_CreateScriptSnapshot(uint8_t** buffer,
 DART_EXPORT Dart_Handle Dart_CreateLibrarySnapshot(Dart_Handle library,
                                                    uint8_t** buffer,
                                                    intptr_t* size) {
+  API_TIMELINE_DURATION;
   return createLibrarySnapshot(library, buffer, size);
 }