Better remove HistoryNodes

content/common/page_state_serialization.cc

Index: content/common/page_state_serialization.cc
diff --git a/content/common/page_state_serialization.cc b/content/common/page_state_serialization.cc
index cff62c36ce39c17bbb25e2dcced684ea6c9dc9d9..77e2abf039387e15caaa1c9a7809e289d3dab615 100644
--- a/content/common/page_state_serialization.cc
+++ b/content/common/page_state_serialization.cc
@@ -195,12 +195,13 @@ struct SerializeObject {
 //     viewport within the unzoomed main frame.
 // 21: Add frame sequence number.
 // 22: Add scroll restoration type.
+// 23: Remove frame sequence number, there are easier ways.
 //
 // NOTE: If the version is -1, then the pickle contains only a URL string.
 // See ReadPageState.
 //
 const int kMinVersion = 11;
-const int kCurrentVersion = 22;
+const int kCurrentVersion = 23;
 
 // A bunch of convenience functions to read/write to SerializeObjects.  The
 // de-serializers assume the input data will be in the correct format and fall
@@ -493,7 +494,6 @@ void WriteFrameState(
   WriteReal(state.page_scale_factor, obj);
   WriteInteger64(state.item_sequence_number, obj);
   WriteInteger64(state.document_sequence_number, obj);
-  WriteInteger64(state.frame_sequence_number, obj);
   WriteInteger(state.referrer_policy, obj);
   WriteReal(state.pinch_viewport_scroll_offset.x(), obj);
   WriteReal(state.pinch_viewport_scroll_offset.y(), obj);
@@ -552,8 +552,8 @@ void ReadFrameState(SerializeObject* obj, bool is_top,
   state->page_scale_factor = ReadReal(obj);
   state->item_sequence_number = ReadInteger64(obj);
   state->document_sequence_number = ReadInteger64(obj);
-  if (obj->version >= 21)
-    state->frame_sequence_number = ReadInteger64(obj);
+  if (obj->version >= 21 && obj->version < 23)
+    ReadInteger64(obj); // Skip obsolete frame sequence number.
 
   if (obj->version >= 17 && obj->version < 19)
     ReadInteger64(obj); // Skip obsolete target frame id number.
@@ -685,7 +685,6 @@ ExplodedFrameState::ExplodedFrameState()
     : scroll_restoration_type(blink::WebHistoryScrollRestorationAuto),
       item_sequence_number(0),
       document_sequence_number(0),
-      frame_sequence_number(0),
       page_scale_factor(0.0),
       referrer_policy(blink::WebReferrerPolicyDefault) {
 }
@@ -713,7 +712,6 @@ void ExplodedFrameState::assign(const ExplodedFrameState& other) {
   scroll_offset = other.scroll_offset;
   item_sequence_number = other.item_sequence_number;
   document_sequence_number = other.document_sequence_number;
-  frame_sequence_number = other.frame_sequence_number;
   page_scale_factor = other.page_scale_factor;
   referrer_policy = other.referrer_policy;
   http_body = other.http_body;