Array length reduction should throw in strict mode if it can't delete an element.

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index 6ef46beef64e6ca8acd7b28d9c6b41f87596ec4a..795b429a924628626d87d34d973b20126a18447e 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -2066,7 +2066,7 @@ class JSObject: public JSReceiver {
                                                    uint32_t limit);
 
   MUST_USE_RESULT static Maybe<bool> SetPropertyWithInterceptor(
-      LookupIterator* it, Handle<Object> value);
+      LookupIterator* it, ShouldThrow should_throw, Handle<Object> value);
 
   // SetLocalPropertyIgnoreAttributes converts callbacks to fields. We need to
   // grant an exemption to AccessorInfo callbacks in some cases.
@@ -2517,7 +2517,7 @@ class JSObject: public JSReceiver {
                               PropertyAttributes attributes);
 
   MUST_USE_RESULT static Maybe<bool> DeletePropertyWithInterceptor(
-      LookupIterator* it);
+      LookupIterator* it, ShouldThrow should_throw);
 
   bool ReferencesObjectFromElements(FixedArray* elements,
                                     ElementsKind kind,