AIX: Fix 'may be used uninitialized' compiler errors

src/layout-descriptor-inl.h

 // Copyright 2014 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_LAYOUT_DESCRIPTOR_INL_H_
 #define V8_LAYOUT_DESCRIPTOR_INL_H_
 
 #include "src/layout-descriptor.h"
 
 namespace v8 {
@@ skipping 44 matching lines @@
   return true;
 }
 
 
 LayoutDescriptor* LayoutDescriptor::SetRawData(int field_index) {
   return SetTagged(field_index, false);
 }
 
 
 LayoutDescriptor* LayoutDescriptor::SetTagged(int field_index, bool tagged) {
-  int layout_word_index;
-  int layout_bit_index;
+  int layout_word_index = 0;
+  int layout_bit_index = 0;
 
   if (!GetIndexes(field_index, &layout_word_index, &layout_bit_index)) {
     CHECK(false);
     return this;
   }
   uint32_t layout_mask = static_cast<uint32_t>(1) << layout_bit_index;
 
   if (IsSlowLayout()) {
     uint32_t value = get_scalar(layout_word_index);
     if (tagged) {
@@ skipping 170 matching lines @@
   // Object headers do not contain non-tagged fields.
   if (offset_in_bytes < header_size_) return true;
   int field_index = (offset_in_bytes - header_size_) / kPointerSize;
 
   return layout_descriptor_->IsTagged(field_index);
 }
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_LAYOUT_DESCRIPTOR_INL_H_