Address review comments

src/google/protobuf/util/field_mask_util.cc

@@ -62,23 +62,23 @@ bool FieldMaskUtil::SnakeCaseToCamelCase(StringPiece input,
                                          std::string* output) {
   output->clear();
   bool after_underscore = false;
-  for (unsigned int i = 0; i < input.size(); ++i) {
-    if (input[i] >= 'A' && input[i] <= 'Z') {
+  for (const char& input_char : input) {
+    if (input_char >= 'A' && input_char <= 'Z') {
       // The field name must not contain uppercase letters.
       return false;
     }
     if (after_underscore) {
-      if (input[i] >= 'a' && input[i] <= 'z') {
-        output->push_back(input[i] + 'A' - 'a');
+      if (input_char >= 'a' && input_char <= 'z') {
+        output->push_back(input_char + 'A' - 'a');
         after_underscore = false;
       } else {
         // The character after a "_" must be a lowercase letter.
         return false;
       }
-    } else if (input[i] == '_') {
+    } else if (input_char == '_') {
       after_underscore = true;
     } else {
-      output->push_back(input[i]);
+      output->push_back(input_char);
     }
   }
   if (after_underscore) {
@@ -331,14 +331,13 @@ void FieldMaskTree::AddPath(const std::string& path) {
   }
   bool new_branch = false;
   Node* node = &root_;
-  for (const std::string& part : parts) {
+  for (const std::string& node_name : parts) {
     if (!new_branch && node != &root_ && node->children.empty()) {
       // Path matches an existing leaf node. This means the path is already
       // covered by this tree (for example, adding "foo.bar.baz" to a tree
       // which already contains "foo.bar").
       return;
     }
-    const std::string& node_name = part;
     Node*& child = node->children[node_name];
     if (child == NULL) {
       new_branch = true;