Add methods to allow resuming execution after calling TerminateExecution().

src/execution.cc

Index: src/execution.cc
===================================================================
--- src/execution.cc	(revision 13939)
+++ src/execution.cc	(working copy)
@@ -425,6 +425,13 @@
 }
 
 
+void StackGuard::CancelTerminateExecution() {
+  ExecutionAccess access(isolate_);
+  Continue(TERMINATE);
+  isolate_->CancelTerminateExecution();
+}
+
+
 void StackGuard::TerminateExecution() {
   ExecutionAccess access(isolate_);
   thread_local_.interrupt_flags_ |= TERMINATE;