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

components/ui_devtools/string_util.h

Index: components/ui_devtools/string_util.h
diff --git a/components/ui_devtools/string_util.h b/components/ui_devtools/string_util.h
index b392ee36d6354a3e74596b2d1bdf5616dd08fb52..5befcac4e88e5082b3ea62ab3432f4a52f6b8d77 100644
--- a/components/ui_devtools/string_util.h
+++ b/components/ui_devtools/string_util.h
@@ -45,9 +45,21 @@ class StringUtil {
   static String fromDouble(double number) {
     return base::DoubleToString(number);
   }
+  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 const size_t kNotFound = static_cast<size_t>(-1);
   static std::unique_ptr<Value> parseJSON(const String& string);
 };