Make blink::protocol::StringBuilder a distinct type from WTF::StringBuilder.

third_party/inspector_protocol/lib/Parser_cpp.template

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 {% for namespace in config.protocol.namespace %}
 namespace {{namespace}} {
 {% endfor %}
 
 namespace {
 
@@ skipping 319 matching lines @@
     DCHECK(false);
     return 0;
 }
 
 template<typename Char>
 bool decodeString(const Char* start, const Char* end, StringBuilder* output)
 {
     while (start < end) {
         uint16_t c = *start++;
         if ('\\' != c) {
-            output->append(c);
+            StringUtil::builderAppend(*output, c);
             continue;
         }
         if (start == end)
             return false;
         c = *start++;
 
         if (c == 'x') {
             // \x is not supported.
             return false;
         }
@@ skipping 24 matching lines @@
         case 'u':
             c = (hexToInt(*start) << 12) +
                 (hexToInt(*(start + 1)) << 8) +
                 (hexToInt(*(start + 2)) << 4) +
                 hexToInt(*(start + 3));
             start += 4;
             break;
         default:
             return false;
         }
-        output->append(c);
+        StringUtil::builderAppend(*output, c);
     }
     return true;
 }
 
 template<typename Char>
 bool decodeString(const Char* start, const Char* end, String* output)
 {
     if (start == end) {
         *output = "";
         return true;
     }
     if (start > end)
         return false;
     StringBuilder buffer;
     StringUtil::builderReserve(buffer, end - start);
     if (!decodeString(start, end, &buffer))
         return false;
-    *output = buffer.toString();
+    *output = StringUtil::builderToString(buffer);
     return true;
 }
 
 template<typename Char>
 std::unique_ptr<Value> buildValue(const Char* start, const Char* end, const Char** valueTokenEnd, int depth)
 {
     if (depth > stackLimit)
         return nullptr;
 
     std::unique_ptr<Value> result;
@@ skipping 130 matching lines @@
 }
 
 std::unique_ptr<Value> parseJSONCharacters(const uint8_t* characters, unsigned length)
 {
     return parseJSONInternal<uint8_t>(characters, length);
 }
 
 {% for namespace in config.protocol.namespace %}
 } // namespace {{namespace}}
 {% endfor %}