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

src/arguments.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_ARGUMENTS_H_
 #define V8_ARGUMENTS_H_
 
 #include "src/allocation.h"
 #include "src/isolate.h"
 
@@ skipping 134 matching lines @@
  public:
   typedef PropertyCallbackInfo<Value> T;
   typedef CustomArguments<T> Super;
   static const int kArgsLength = T::kArgsLength;
   static const int kThisIndex = T::kThisIndex;
   static const int kHolderIndex = T::kHolderIndex;
   static const int kDataIndex = T::kDataIndex;
   static const int kReturnValueDefaultValueIndex =
       T::kReturnValueDefaultValueIndex;
   static const int kIsolateIndex = T::kIsolateIndex;
+  static const int kShouldThrowOnErrorIndex = T::kShouldThrowOnErrorIndex;
 
-  PropertyCallbackArguments(Isolate* isolate,
-                            Object* data,
-                            Object* self,
-                            JSObject* holder)
+  PropertyCallbackArguments(Isolate* isolate, Object* data, Object* self,
+                            JSObject* holder, Object::ShouldThrow should_throw)
       : Super(isolate) {
     Object** values = this->begin();
     values[T::kThisIndex] = self;
     values[T::kHolderIndex] = holder;
     values[T::kDataIndex] = data;
     values[T::kIsolateIndex] = reinterpret_cast<Object*>(isolate);
+    values[T::kShouldThrowOnErrorIndex] =
+        Smi::FromInt(should_throw == Object::THROW_ON_ERROR ? 1 : 0);
+
     // Here the hole is set as default value.
     // It cannot escape into js as it's remove in Call below.
     values[T::kReturnValueDefaultValueIndex] =
         isolate->heap()->the_hole_value();
     values[T::kReturnValueIndex] = isolate->heap()->the_hole_value();
     DCHECK(values[T::kHolderIndex]->IsHeapObject());
     DCHECK(values[T::kIsolateIndex]->IsSmi());
   }
 
   /*
@@ skipping 109 matching lines @@
 #define RUNTIME_FUNCTION(Name) RUNTIME_FUNCTION_RETURNS_TYPE(Object*, Name)
 #define RUNTIME_FUNCTION_RETURN_PAIR(Name) \
     RUNTIME_FUNCTION_RETURNS_TYPE(ObjectPair, Name)
 #define RUNTIME_FUNCTION_RETURN_TRIPLE(Name) \
     RUNTIME_FUNCTION_RETURNS_TYPE(ObjectTriple, Name)
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_ARGUMENTS_H_