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

base/ref_counted_memory.h

Index: base/ref_counted_memory.h
===================================================================
--- base/ref_counted_memory.h	(revision 30122)
+++ base/ref_counted_memory.h	(working copy)
@@ -19,7 +19,8 @@
  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.
@@ -64,7 +65,11 @@
   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;