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

third_party/protobuf/src/google/protobuf/compiler/cpp/cpp_string_field.h

Index: third_party/protobuf/src/google/protobuf/compiler/cpp/cpp_string_field.h
diff --git a/third_party/protobuf/src/google/protobuf/compiler/cpp/cpp_string_field.h b/third_party/protobuf/src/google/protobuf/compiler/cpp/cpp_string_field.h
index 616e20674f70dc7aad12e1d3e943e50c49c9b1f4..cb4e8772d00725e8ed67470d6d397306b3398a67 100644
--- a/third_party/protobuf/src/google/protobuf/compiler/cpp/cpp_string_field.h
+++ b/third_party/protobuf/src/google/protobuf/compiler/cpp/cpp_string_field.h
@@ -46,8 +46,8 @@ namespace cpp {
 
 class StringFieldGenerator : public FieldGenerator {
  public:
-  explicit StringFieldGenerator(const FieldDescriptor* descriptor,
-                                const Options& options);
+  StringFieldGenerator(const FieldDescriptor* descriptor,
+                       const Options& options);
   ~StringFieldGenerator();
 
   // implements FieldGenerator ---------------------------------------
@@ -79,8 +79,8 @@ class StringFieldGenerator : public FieldGenerator {
 
 class StringOneofFieldGenerator : public StringFieldGenerator {
  public:
-  explicit StringOneofFieldGenerator(const FieldDescriptor* descriptor,
-                                     const Options& options);
+  StringOneofFieldGenerator(const FieldDescriptor* descriptor,
+                            const Options& options);
   ~StringOneofFieldGenerator();
 
   // implements FieldGenerator ---------------------------------------
@@ -99,8 +99,8 @@ class StringOneofFieldGenerator : public StringFieldGenerator {
 
 class RepeatedStringFieldGenerator : public FieldGenerator {
  public:
-  explicit RepeatedStringFieldGenerator(const FieldDescriptor* descriptor,
-                                        const Options& options);
+  RepeatedStringFieldGenerator(const FieldDescriptor* descriptor,
+                               const Options& options);
   ~RepeatedStringFieldGenerator();
 
   // implements FieldGenerator ---------------------------------------