Add a target_frame_id to the history serialization format.

content/public/renderer/history_item_serialization.cc

Index: content/public/renderer/history_item_serialization.cc
diff --git a/content/public/renderer/history_item_serialization.cc b/content/public/renderer/history_item_serialization.cc
index 6bef7de3f3c392fa8bb50f6ab5791e21e253e6fb..9ca41350c4218410ff2b6a448c467a310871b450 100644
--- a/content/public/renderer/history_item_serialization.cc
+++ b/content/public/renderer/history_item_serialization.cc
@@ -91,6 +91,7 @@ bool RecursivelyGenerateFrameState(const WebHistoryItem& item,
   state->item_sequence_number = item.itemSequenceNumber();
   state->document_sequence_number =
       item.documentSequenceNumber();
+  state->target_frame_id = item.targetFrameID();
   state->page_scale_factor = item.pageScaleFactor();
   ToNullableString16Vector(item.documentState(), &state->document_state);
 
@@ -139,6 +140,8 @@ bool RecursivelyGenerateHistoryItem(const ExplodedFrameState& state,
   if (state.document_sequence_number)
     item->setDocumentSequenceNumber(state.document_sequence_number);
 
+  item->setTargetFrameID(state.target_frame_id);
+
   item->setHTTPContentType(state.http_body.http_content_type);
   if (!state.http_body.is_null) {
     WebHTTPBody http_body;