[runtime] Speed up C++ version of ArrayPush

src/debug/liveedit.cc

 // 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.
 
 #include "src/debug/liveedit.h"
 
 #include "src/ast/scopeinfo.h"
 #include "src/ast/scopes.h"
 #include "src/code-stubs.h"
 #include "src/compilation-cache.h"
@@ skipping 1891 matching lines @@
     Handle<JSArray> old_shared_array, Handle<JSArray> new_shared_array,
     bool do_drop) {
   Isolate* isolate = old_shared_array->GetIsolate();
   int len = GetArrayLength(old_shared_array);
 
   DCHECK(old_shared_array->HasFastElements());
   Handle<FixedArray> old_shared_array_elements(
       FixedArray::cast(old_shared_array->elements()));
 
   Handle<JSArray> result = isolate->factory()->NewJSArray(len);
+  JSObject::EnsureWritableFastElements(result);
   Handle<FixedArray> result_elements =
-      JSObject::EnsureWritableFastElements(result);
+      handle(FixedArray::cast(result->elements()), isolate);
 
   // Fill the default values.
   for (int i = 0; i < len; i++) {
     FunctionPatchabilityStatus status = FUNCTION_AVAILABLE_FOR_PATCH;
     result_elements->set(i, Smi::FromInt(status));
   }
 
   // Scan the heap for active generators -- those that are either currently
   // running (as we wouldn't want to restart them, because we don't know where
   // to restart them from) or suspended.  Fail if any one corresponds to the set
@@ skipping 113 matching lines @@
   isolate_->active_function_info_listener()->FunctionCode(code);
 }
 
 
 bool LiveEditFunctionTracker::IsActive(Isolate* isolate) {
   return isolate->active_function_info_listener() != NULL;
 }
 
 }  // namespace internal
 }  // namespace v8