Add the rate of js invocations from the api as a signal of idleness

test/cctest/cctest.h

Index: test/cctest/cctest.h
diff --git a/test/cctest/cctest.h b/test/cctest/cctest.h
index a0bc09d95062cbbc9a8b12799b4fb37a2106acf5..9798dfbc3c14612d05b30cb2276903bebb3b285b 100644
--- a/test/cctest/cctest.h
+++ b/test/cctest/cctest.h
@@ -530,6 +530,13 @@ static inline void DisableInlineAllocationSteps(v8::internal::NewSpace* space) {
 }
 
 
+static inline void CheckDoubleEquals(double expected, double actual) {
+  const double kEpsilon = 1e-10;
+  CHECK_LE(expected, actual + kEpsilon);
+  CHECK_GE(expected, actual - kEpsilon);
+}
+
+
 static int LenFromSize(int size) {
   return (size - i::FixedArray::kHeaderSize) / i::kPointerSize;
 }