Update //third_party/protobuf to version 3.

third_party/protobuf/csharp/protos/unittest_issues.proto

+syntax = "proto3";
+
+// These proto descriptors have at one time been reported as an issue or defect.
+// They are kept here to replicate the issue, and continue to verify the fix.
+
+// Issue: Non-"Google.Protobuffers" namespace will ensure that protobuffer library types are qualified
+option csharp_namespace = "UnitTest.Issues.TestProtos";
+
+package unittest_issues;
+option optimize_for = SPEED;
+
+// Issue 307: when generating doubly-nested types, any references
+// should be of the form A.Types.B.Types.C.
+message Issue307 {
+  message NestedOnce {
+    message NestedTwice {
+    }
+  }
+}
+
+// Old issue 13: http://code.google.com/p/protobuf-csharp-port/issues/detail?id=13
+// New issue 309: https://github.com/google/protobuf/issues/309
+ 
+// message A {
+//    optional int32 _A = 1;
+// }
+
+// message B {
+//    optional int32 B_ = 1;
+// }
+
+//message AB {
+//    optional int32 a_b = 1;
+//}
+
+// Similar issue with numeric names
+// Java code failed too, so probably best for this to be a restriction.
+// See https://github.com/google/protobuf/issues/308
+// message NumberField {
+//    optional int32 _01 = 1;
+// }
+
+// issue 19 - negative enum values
+
+enum NegativeEnum {
+    NEGATIVE_ENUM_ZERO = 0;
+    FiveBelow = -5;
+    MinusOne = -1;
+}
+
+message NegativeEnumMessage {
+    NegativeEnum value = 1;
+    repeated NegativeEnum values = 2 [packed = false];
+    repeated NegativeEnum packed_values = 3 [packed=true];
+}
+
+// Issue 21: http://code.google.com/p/protobuf-csharp-port/issues/detail?id=21
+// Decorate fields with [deprecated=true] as [System.Obsolete]
+
+message DeprecatedChild {
+}
+
+enum DeprecatedEnum {
+    DEPRECATED_ZERO = 0;
+    one = 1;
+}
+
+message DeprecatedFieldsMessage {
+    int32 PrimitiveValue = 1 [deprecated = true];
+    repeated int32 PrimitiveArray = 2 [deprecated = true];
+
+    DeprecatedChild MessageValue = 3 [deprecated = true];
+    repeated DeprecatedChild MessageArray = 4 [deprecated = true];
+
+    DeprecatedEnum EnumValue = 5 [deprecated = true];
+    repeated DeprecatedEnum EnumArray = 6 [deprecated = true];
+}
+
+// Issue 45: http://code.google.com/p/protobuf-csharp-port/issues/detail?id=45
+message ItemField {
+  int32 item = 1;
+}
+
+message ReservedNames {
+  // Force a nested type called Types
+  message SomeNestedType {
+  }
+
+  int32 types = 1;
+  int32 descriptor = 2;
+}
+
+message TestJsonFieldOrdering {
+  // These fields are deliberately not declared in numeric
+  // order, and the oneof fields aren't contiguous either.
+  // This allows for reasonably robust tests of JSON output
+  // ordering.
+  // TestFieldOrderings in unittest_proto3.proto is similar,
+  // but doesn't include oneofs.
+  // TODO: Consider adding oneofs to TestFieldOrderings, although
+  // that will require fixing other tests in multiple platforms.
+  // Alternatively, consider just adding this to
+  // unittest_proto3.proto if multiple platforms want it.
+  
+  int32 plain_int32 = 4;
+
+  oneof o1 {
+    string o1_string = 2;
+    int32 o1_int32 = 5;
+  }
+  
+  string plain_string = 1;
+  
+  oneof o2 {
+    int32 o2_int32 = 6;
+    string o2_string = 3;
+  }
+  
+}