Add InvokeApiInterruptCallbacks runtime counter

This was one of the paths inside StackGuard that lacked a runtime counter,
making it hard to assess what was going on.

BUG=

Review-Url: https://codereview.chromium.org/2346863002
Cr-Commit-Position: refs/heads/master@{#39455}

src/counters.h

@@ -691,6 +691,7 @@ class RuntimeCallTimer {
   V(IndexedPropertyGetterCallback)                  \
   V(IndexedPropertyQueryCallback)                   \
   V(IndexedPropertySetterCallback)                  \
+  V(InvokeApiInterruptCallbacks)                    \
   V(InvokeFunctionCallback)                         \
   V(JS_Execution)                                   \
   V(Map_SetPrototype)                               \

src/isolate.cc

@@ -979,6 +979,8 @@ void Isolate::RequestInterrupt(InterruptCallback callback, void* data) {
 
 
 void Isolate::InvokeApiInterruptCallbacks() {
+  RuntimeCallTimerScope runtimeTimer(
+      this, &RuntimeCallStats::InvokeApiInterruptCallbacks);
   // Note: callback below should be called outside of execution access lock.
   while (true) {
     InterruptEntry entry;