Update protobuf to r428, part 1.

third_party/protobuf/src/google/protobuf/stubs/map-util.h

Index: third_party/protobuf/src/google/protobuf/stubs/map-util.h
===================================================================
--- third_party/protobuf/src/google/protobuf/stubs/map-util.h	(revision 216642)
+++ third_party/protobuf/src/google/protobuf/stubs/map-util.h	(working copy)
@@ -68,6 +68,30 @@
   return &it->second;
 }
 
+// Perform a lookup in a map or hash_map, assuming that the key exists.
+// Crash if it does not.
+//
+// This is intended as a replacement for operator[] as an rvalue (for reading)
+// when the key is guaranteed to exist.
+//
+// operator[] is discouraged for several reasons:
+//  * It has a side-effect of inserting missing keys
+//  * It is not thread-safe (even when it is not inserting, it can still
+//      choose to resize the underlying storage)
+//  * It invalidates iterators (when it chooses to resize)
+//  * It default constructs a value object even if it doesn't need to
+//
+// This version assumes the key is printable, and includes it in the fatal log
+// message.
+template <class Collection>
+const typename Collection::value_type::second_type&
+FindOrDie(const Collection& collection,
+          const typename Collection::value_type::first_type& key) {
+  typename Collection::const_iterator it = collection.find(key);
+  GOOGLE_CHECK(it != collection.end()) << "Map key not found: " << key;
+  return it->second;
+}
+
 // Perform a lookup in a map or hash_map whose values are pointers.
 // If the key is present a const pointer to the associated value is returned,
 // otherwise a NULL pointer is returned.