Fix an exception in the ref counted data. This appeares as a crash on startip...

base/ref_counted_memory.h

 // Copyright (c) 2009 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.
 
 #ifndef BASE_REF_COUNTED_MEMORY_H_
 #define BASE_REF_COUNTED_MEMORY_H_
 
 #include <vector>
 
 #include "base/ref_counted.h"
 
 // TODO(erg): The contents of this file should be in a namespace. This would
 // require touching >100 files in chrome/ though.
 
 // A generic interface to memory. This object is reference counted because one
 // of its two subclasses own the data they carry, and we need to have
 // heterogeneous containers of these two types of memory.
 class RefCountedMemory : public base::RefCountedThreadSafe< RefCountedMemory > {
  public:
   virtual ~RefCountedMemory() {}
 
-  // Retrieves a pointer to the beginning of the data we point to.
+  // Retrieves a pointer to the beginning of the data we point to. If the data
+  // is empty, this will return NULL.
   virtual const unsigned char* front() const = 0;
 
   // Size of the memory pointed to.
   virtual size_t size() const = 0;
 };
 
 // An implementation of RefCountedMemory, where the ref counting does not
 // matter.
 class RefCountedStaticMemory : public RefCountedMemory {
  public:
@@ skipping 24 matching lines @@
     bytes->data.swap(*to_destroy);
     return bytes;
   }
 
   RefCountedBytes() {}
 
   // Constructs a RefCountedBytes object by _copying_ from |initializer|.
   RefCountedBytes(const std::vector<unsigned char>& initializer)
       : data(initializer) {}
 
-  virtual const unsigned char* front() const { return &data.front(); }
+  virtual const unsigned char* front() const {
+    // STL will assert if we do front() on an empty vector, but calling code
+    // expects a NULL.
+    return size() ? &data.front() : NULL;
+  }
   virtual size_t size() const { return data.size(); }
 
   std::vector<unsigned char> data;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(RefCountedBytes);
 };
 
 #endif  // BASE_REF_COUNTED_MEMORY_H_