Add attributions so printf like functions can have their arguments checked.

runtime/vm/snapshot_test.cc

Index: runtime/vm/snapshot_test.cc
diff --git a/runtime/vm/snapshot_test.cc b/runtime/vm/snapshot_test.cc
index d331836f84f924c08bc5e54609c05a90afb6ac34..33ed7a063b1a819accfd15a8ff96d4c760b92fd0 100644
--- a/runtime/vm/snapshot_test.cc
+++ b/runtime/vm/snapshot_test.cc
@@ -800,7 +800,7 @@ UNIT_TEST_CASE(FullSnapshot) {
     // Create a test library and Load up a test script in it.
     TestCase::LoadTestScript(kScriptChars, NULL);
     timer1.Stop();
-    OS::PrintErr("Without Snapshot: %dus\n", timer1.TotalElapsedTime());
+    OS::PrintErr("Without Snapshot: %"Pd64"us\n", timer1.TotalElapsedTime());
 
     // Write snapshot with object content.
     Isolate* isolate = Isolate::Current();
@@ -818,7 +818,7 @@ UNIT_TEST_CASE(FullSnapshot) {
   {
     Dart_EnterScope();  // Start a Dart API scope for invoking API functions.
     timer2.Stop();
-    OS::PrintErr("From Snapshot: %dus\n", timer2.TotalElapsedTime());
+    OS::PrintErr("From Snapshot: %"Pd64"us\n", timer2.TotalElapsedTime());
 
     // Invoke a function which returns an object.
     Dart_Handle cls =
@@ -857,7 +857,7 @@ UNIT_TEST_CASE(FullSnapshot1) {
     Dart_Handle lib = TestCase::LoadTestScript(kScriptChars, NULL);
     ClassFinalizer::FinalizePendingClasses();
     timer1.Stop();
-    OS::PrintErr("Without Snapshot: %dus\n", timer1.TotalElapsedTime());
+    OS::PrintErr("Without Snapshot: %"Pd64"us\n", timer1.TotalElapsedTime());
 
     // Write snapshot with object content.
     FullSnapshotWriter writer(&buffer, &malloc_allocator);
@@ -877,7 +877,7 @@ UNIT_TEST_CASE(FullSnapshot1) {
   {
     Dart_EnterScope();  // Start a Dart API scope for invoking API functions.
     timer2.Stop();
-    OS::PrintErr("From Snapshot: %dus\n", timer2.TotalElapsedTime());
+    OS::PrintErr("From Snapshot: %"Pd64"us\n", timer2.TotalElapsedTime());
 
     // Invoke a function which returns an object.
     Dart_Handle cls = Dart_GetClass(TestCase::lib(),