Introduce API to temporarily interrupt long running JavaScript code.

src/execution.h

Index: src/execution.h
diff --git a/src/execution.h b/src/execution.h
index eda416c0da5409f82e9dda4bbbb749d24bf0ea01..3e62d8730ab471bc71f9d0ce5dc603be0356854e 100644
--- a/src/execution.h
+++ b/src/execution.h
@@ -43,7 +43,8 @@ enum InterruptFlag {
   TERMINATE = 1 << 4,
   GC_REQUEST = 1 << 5,
   FULL_DEOPT = 1 << 6,
-  INSTALL_CODE = 1 << 7
+  INSTALL_CODE = 1 << 7,
+  API_INTERRUPT = 1 << 8
 };
 
 
@@ -222,6 +223,11 @@ class StackGuard {
   void FullDeopt();
   void Continue(InterruptFlag after_what);
 
+  void RequestInterrupt(InterruptCallback callback, void* data);
+  void ClearInterrupt();
+  bool IsAPIInterrupt();
+  void InvokeInterruptCallback();
+
   // This provides an asynchronous read of the stack limits for the current
   // thread.  There are no locks protecting this, but it is assumed that you
   // have the global V8 lock if you are using multiple V8 threads.
@@ -307,6 +313,9 @@ class StackGuard {
     int nesting_;
     int postpone_interrupts_nesting_;
     int interrupt_flags_;
+
+    InterruptCallback interrupt_callback_;
+    void* interrupt_callback_data_;
   };
 
   // TODO(isolates): Technically this could be calculated directly from a