Add merge rules for first read time

components/reading_list/ios/reading_list_entry.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "components/reading_list/ios/reading_list_entry.h"
 
 #include "base/json/json_string_value_serializer.h"
 #include "base/memory/ptr_util.h"
 #include "components/reading_list/ios/offline_url_utils.h"
 #include "components/reading_list/ios/proto/reading_list.pb.h"
@@ skipping 306 matching lines @@
     title = pb_entry.title();
   }
 
   int64_t creation_time_us = 0;
   if (pb_entry.has_creation_time_us()) {
     creation_time_us = pb_entry.creation_time_us();
   }
 
   int64_t first_read_time_us = 0;
   if (pb_entry.has_first_read_time_us()) {
-    creation_time_us = pb_entry.first_read_time_us();
+    first_read_time_us = pb_entry.first_read_time_us();
   }
 
   int64_t update_time_us = 0;
   if (pb_entry.has_update_time_us()) {
     update_time_us = pb_entry.update_time_us();
   }
 
   State state = UNSEEN;
   if (pb_entry.has_status()) {
     switch (pb_entry.status()) {
@@ skipping 23 matching lines @@
       other.AsReadingListSpecifics());
 #endif
   DCHECK(url_ == other.url_);
   if (title_.compare(other.title_) < 0) {
     // Take the last in alphabetical order or the longer one.
     // This ensure empty string is replaced.
     title_ = std::move(other.title_);
   }
   if (creation_time_us_ < other.creation_time_us_) {
     creation_time_us_ = std::move(other.creation_time_us_);
-  }
-  if (state_ == UNSEEN) {
-    state_ = std::move(other.state_);
-  } else if (other.state_ != UNSEEN) {
-    // Both are not UNSEEN, take the newer one.
-    if (update_time_us_ < other.update_time_us_) {
-      state_ = std::move(other.state_);
-    } else if (update_time_us_ == other.update_time_us_) {
-      // Both states are likely the same, but if they are not, READ should win.
-      if (other.state_ == READ) {
-        state_ = std::move(other.state_);
-      }
+    first_read_time_us_ = std::move(other.first_read_time_us_);
+  } else if (creation_time_us_ == other.creation_time_us_) {
+    // The first_time_read_us from |other| is used if
+    // - this.first_time_read_us == 0: the entry was never read in this device.
+    // - this.first_time_read_us > other.first_time_read_us: the entry was
+    //       first read on another device.
+    if (first_read_time_us_ == 0 ||
+        (other.first_read_time_us_ != 0 &&
+         other.first_read_time_us_ < first_read_time_us_)) {
+      first_read_time_us_ = std::move(other.first_read_time_us_);
     }
   }
   if (update_time_us_ < other.update_time_us_) {
     update_time_us_ = std::move(other.update_time_us_);
+    state_ = std::move(other.state_);
+  } else if (update_time_us_ == other.update_time_us_) {
+    if (state_ == UNSEEN) {
+      state_ = std::move(other.state_);
+    } else if (other.state_ == READ) {
+      state_ = std::move(other.state_);
+    }
   }
 #if !defined(NDEBUG)
   std::unique_ptr<sync_pb::ReadingListSpecifics> new_this_pb(
       AsReadingListSpecifics());
   DCHECK(ReadingListStore::CompareEntriesForSync(*old_this_pb, *new_this_pb));
   DCHECK(ReadingListStore::CompareEntriesForSync(*other_pb, *new_this_pb));
 #endif
 }
 
 std::unique_ptr<reading_list::ReadingListLocal>
@@ skipping 80 matching lines @@
     case UNREAD:
       pb_entry->set_status(sync_pb::ReadingListSpecifics::UNREAD);
       break;
     case UNSEEN:
       pb_entry->set_status(sync_pb::ReadingListSpecifics::UNSEEN);
       break;
   }
 
   return pb_entry;
 }