Allow for embedder provided service request handlers

runtime/platform/json.cc

Index: runtime/platform/json.cc
diff --git a/runtime/platform/json.cc b/runtime/platform/json.cc
index 31ad4188f7162196125c79c97d1613182a85a0b3..a406e7a5728bf96303387fbaa070c0e2af6f55a0 100644
--- a/runtime/platform/json.cc
+++ b/runtime/platform/json.cc
@@ -510,6 +510,15 @@ void TextBuffer::Clear() {
 }
 
 
+const char* TextBuffer::Steal() {
+  const char* r = buf_;
+  buf_ = NULL;
+  buf_size_ = 0;
+  msg_len_ = 0;
+  return r;
+}
+
+
 void TextBuffer::AddChar(char ch) {
   EnsureCapacity(sizeof(ch));
   buf_[msg_len_] = ch;