Do not count invocations but usage of a function, i.e., increment a function's counter at IC calls …

tests/language/src/MathVMTest.dart

Index: tests/language/src/MathVMTest.dart
===================================================================
--- tests/language/src/MathVMTest.dart	(revision 4582)
+++ tests/language/src/MathVMTest.dart	(working copy)
@@ -2,7 +2,7 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 // Tests that the VM does not crash on weird corner cases of class Math.
-// VMOptions=--optimization_invocation_threshold=100
+// VMOptions=--optimization_counter_threshold=100
 
 class FakeNumber {
   const FakeNumber();