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

content/browser/devtools/protocol_string.h

Index: content/browser/devtools/protocol_string.h
diff --git a/content/browser/devtools/protocol_string.h b/content/browser/devtools/protocol_string.h
index 1d3d2edf13478fbbcd59d01e783e42870dfbf412..8620823984a0157e9cf4b3940fcc36f426ebc22d 100644
--- a/content/browser/devtools/protocol_string.h
+++ b/content/browser/devtools/protocol_string.h
@@ -53,9 +53,21 @@ class CONTENT_EXPORT StringUtil {
     return s;
   }
   static const size_t kNotFound = static_cast<size_t>(-1);
+  static void builderAppend(StringBuilder& builder, const String& s) {
+    builder.append(s);
+  }
+  static void builderAppend(StringBuilder& builder, char c) {
+    builder.append(c);
+  }
+  static void builderAppend(StringBuilder& builder, const char* s, size_t len) {
+    builder.append(s, len);
+  }
   static void builderReserve(StringBuilder& builder, unsigned capacity) {
     builder.reserveCapacity(capacity);
   }
+  static String builderToString(StringBuilder& builder) {
+    return builder.toString();
+  }
   static std::unique_ptr<protocol::Value> parseJSON(const String&);
 };