Make mojo buffer allocators more robust.

mojo/public/cpp/bindings/lib/fixed_buffer.cc

 // Copyright 2014 The Chromium 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 "mojo/public/cpp/bindings/lib/fixed_buffer.h"
 
 #include <assert.h>
 #include <stdlib.h>
 #include <string.h>
 
 #include <algorithm>
 
 #include "mojo/public/cpp/bindings/lib/bindings_serialization.h"
 
 namespace mojo {
 namespace internal {
 
 FixedBuffer::FixedBuffer(size_t size)
     : ptr_(NULL),
       cursor_(0),
       size_(internal::Align(size)) {
+  // calloc() required to zero memory and thus avoid info leaks.
   ptr_ = static_cast<char*>(calloc(size_, 1));
 }
 
 FixedBuffer::~FixedBuffer() {
   free(ptr_);
 }
 
 void* FixedBuffer::Allocate(size_t delta, Destructor dtor) {
   assert(!dtor);
 
@@ skipping 13 matching lines @@
 void* FixedBuffer::Leak() {
   char* ptr = ptr_;
   ptr_ = NULL;
   cursor_ = 0;
   size_ = 0;
   return ptr;
 }
 
 }  // namespace internal
 }  // namespace mojo