Move stack unwinding logic into the runtime.

src/runtime/runtime-internal.cc

Index: src/runtime/runtime-internal.cc
diff --git a/src/runtime/runtime-internal.cc b/src/runtime/runtime-internal.cc
index 33234cd19f73b7b582a201a6c9158f349376ca36..d701561c2f9d7ac2463be00bfab1e016f9a87e5d 100644
--- a/src/runtime/runtime-internal.cc
+++ b/src/runtime/runtime-internal.cc
@@ -26,7 +26,6 @@ RUNTIME_FUNCTION(Runtime_CheckIsBootstrapping) {
 RUNTIME_FUNCTION(Runtime_Throw) {
   HandleScope scope(isolate);
   DCHECK(args.length() == 1);
-
   return isolate->Throw(args[0]);
 }
 
@@ -34,11 +33,17 @@ RUNTIME_FUNCTION(Runtime_Throw) {
 RUNTIME_FUNCTION(Runtime_ReThrow) {
   HandleScope scope(isolate);
   DCHECK(args.length() == 1);
-
   return isolate->ReThrow(args[0]);
 }
 
 
+RUNTIME_FUNCTION(Runtime_FindExceptionHandler) {
+  SealHandleScope shs(isolate);
+  DCHECK(args.length() == 0);
+  return isolate->FindHandler();
+}
+
+
 RUNTIME_FUNCTION(Runtime_PromoteScheduledException) {
   SealHandleScope shs(isolate);
   DCHECK(args.length() == 0);