Fixed a couple of proxies-related unhandled exceptions.

src/runtime/runtime-scopes.cc

Index: src/runtime/runtime-scopes.cc
diff --git a/src/runtime/runtime-scopes.cc b/src/runtime/runtime-scopes.cc
index 700925db622d718cd1497707de9058aa6c691337..d2d202c08d7b856fd91fe7c1a8e49602105b27b5 100644
--- a/src/runtime/runtime-scopes.cc
+++ b/src/runtime/runtime-scopes.cc
@@ -230,6 +230,8 @@ RUNTIME_FUNCTION(Runtime_DeclareLookupSlot) {
   BindingFlags binding_flags;
   Handle<Object> holder =
       context->Lookup(name, flags, &index, &attributes, &binding_flags);
+  // In case of JSProxy, an exception might have been thrown.
+  if (isolate->has_pending_exception()) return isolate->heap()->exception();

[Yang, 2015/07/08 07:55:18]

This looks hacky. I.e. we should have returned a MaybeHandle.

But then again this is proxy, so I guess I'm fine with this. Can we first check
for holder.is_null() first like we do below?

 
   Handle<JSObject> object;
   Handle<Object> value =
@@ -308,6 +310,8 @@ RUNTIME_FUNCTION(Runtime_InitializeLegacyConstLookupSlot) {
   BindingFlags binding_flags;
   Handle<Object> holder =
       context->Lookup(name, flags, &index, &attributes, &binding_flags);
+  // In case of JSProxy, an exception might have been thrown.
+  if (isolate->has_pending_exception()) return isolate->heap()->exception();
 
   if (index >= 0) {
     DCHECK(holder->IsContext());
@@ -855,6 +859,8 @@ RUNTIME_FUNCTION(Runtime_DeleteLookupSlot) {
 
   // If the slot was not found the result is true.
   if (holder.is_null()) {
+    // In case of JSProxy, an exception might have been thrown.
+    if (isolate->has_pending_exception()) return isolate->heap()->exception();
     return isolate->heap()->true_value();
   }