Update third_party/protobuf to protobuf-v3.0.0-beta-3

third_party/protobuf/csharp/src/Google.Protobuf/WellKnownTypes/ValuePartial.cs

Index: third_party/protobuf/csharp/src/Google.Protobuf/WellKnownTypes/ValuePartial.cs
diff --git a/third_party/protobuf/csharp/src/Google.Protobuf/WellKnownTypes/ValuePartial.cs b/third_party/protobuf/csharp/src/Google.Protobuf/WellKnownTypes/ValuePartial.cs
index b4b6c05e87c18e7abc1ac4e0b96b09a7a546db6f..d34b560de04ccc1d18dd2fb259395dc2718bdb80 100644
--- a/third_party/protobuf/csharp/src/Google.Protobuf/WellKnownTypes/ValuePartial.cs
+++ b/third_party/protobuf/csharp/src/Google.Protobuf/WellKnownTypes/ValuePartial.cs
@@ -41,7 +41,7 @@ namespace Google.Protobuf.WellKnownTypes
         /// <returns>A newly-created Value message with the given value.</returns>
         public static Value ForString(string value)
         {
-            Preconditions.CheckNotNull(value, "value");
+            ProtoPreconditions.CheckNotNull(value, "value");
             return new Value { StringValue = value };
         }
 
@@ -81,7 +81,7 @@ namespace Google.Protobuf.WellKnownTypes
         /// <returns>A newly-created Value message an initial list value.</returns>
         public static Value ForList(params Value[] values)
         {
-            Preconditions.CheckNotNull(values, "values");
+            ProtoPreconditions.CheckNotNull(values, "values");
             return new Value { ListValue = new ListValue { Values = { values } } };
         }
 
@@ -92,7 +92,7 @@ namespace Google.Protobuf.WellKnownTypes
         /// <returns>A newly-created Value message an initial struct value.</returns>
         public static Value ForStruct(Struct value)
         {
-            Preconditions.CheckNotNull(value, "value");
+            ProtoPreconditions.CheckNotNull(value, "value");
             return new Value { StructValue = value };
         }
     }