[Sync] Ensure referrer is recorded regardless of policy conversion

components/sessions/core/serialized_navigation_entry.cc

Index: components/sessions/core/serialized_navigation_entry.cc
diff --git a/components/sessions/core/serialized_navigation_entry.cc b/components/sessions/core/serialized_navigation_entry.cc
index ca686b0add4feaa9f0568128ead68ed1b5836604..3dda4ae452bb051173dcc5eb57535f1d54a2ed89 100644
--- a/components/sessions/core/serialized_navigation_entry.cc
+++ b/components/sessions/core/serialized_navigation_entry.cc
@@ -6,6 +6,7 @@
 
 #include <stddef.h>
 
+#include "base/macros.h"
 #include "base/pickle.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/trace_event/memory_usage_estimator.h"
@@ -18,6 +19,9 @@ namespace sessions {
 // TODO(treib): Remove, not needed anymore. crbug.com/627747
 const char kSearchTermsKey[] = "search_terms";
 
+// The previous referrer policy value corresponding to |Never|.
+const int kObsoleteReferrerPolicyNever = 2;
+
 SerializedNavigationEntry::SerializedNavigationEntry()
     : index_(-1),
       unique_id_(0),
@@ -48,14 +52,8 @@ SerializedNavigationEntry SerializedNavigationEntry::FromSyncData(
     navigation.referrer_url_ = GURL(sync_data.referrer());
     navigation.referrer_policy_ = sync_data.correct_referrer_policy();
   } else {
-    int mapped_referrer_policy;
-    if (SerializedNavigationDriver::Get()->MapReferrerPolicyToNewValues(
-            sync_data.obsolete_referrer_policy(), &mapped_referrer_policy)) {
-      navigation.referrer_url_ = GURL(sync_data.referrer());
-    } else {
-      navigation.referrer_url_ = GURL();
-    }
-    navigation.referrer_policy_ = mapped_referrer_policy;
+    navigation.referrer_url_ = GURL();
+    navigation.referrer_policy_ = kObsoleteReferrerPolicyNever;
   }
   navigation.virtual_url_ = GURL(sync_data.virtual_url());
   navigation.title_ = base::UTF8ToUTF16(sync_data.title());
@@ -236,15 +234,11 @@ void SerializedNavigationEntry::WriteToPickle(int max_size,
   const int type_mask = has_post_data_ ? HAS_POST_DATA : 0;
   pickle->WriteInt(type_mask);
 
-  int mapped_referrer_policy;
-  if (SerializedNavigationDriver::Get()->MapReferrerPolicyToOldValues(
-          referrer_policy_, &mapped_referrer_policy) &&
-      referrer_url_.is_valid()) {
-    WriteStringToPickle(pickle, &bytes_written, max_size, referrer_url_.spec());
-  } else {
-    WriteStringToPickle(pickle, &bytes_written, max_size, std::string());
-  }
-  pickle->WriteInt(mapped_referrer_policy);
+  WriteStringToPickle(pickle, &bytes_written, max_size, referrer_url_.spec());
+
+  // This field was deprecated in m61, but we still write it to the pickle for
+  // forwards compatibility.
+  pickle->WriteInt(kObsoleteReferrerPolicyNever);
 
   // Save info required to override the user agent.
   WriteStringToPickle(
@@ -294,15 +288,11 @@ bool SerializedNavigationEntry::ReadFromPickle(base::PickleIterator* iterator) {
       referrer_spec = std::string();
     referrer_url_ = GURL(referrer_spec);
 
-    // The "referrer policy" property was added even later, so we fall back to
-    // the default policy if the property is not present.
-    //
-    // Note: due to crbug.com/450589 this value might be incorrect, and a
-    // corrected version is stored later in the pickle.
-    if (!iterator->ReadInt(&referrer_policy_)) {
-      referrer_policy_ =
-          SerializedNavigationDriver::Get()->GetDefaultReferrerPolicy();
-    }
+    // Note: due to crbug.com/450589 the initial referrer policy is incorrect,
+    // and ignored. A correct referrer policy is extracted later (see
+    // |correct_referrer_policy| below).
+    int ignored_referrer_policy;
+    ignore_result(iterator->ReadInt(&ignored_referrer_policy));
 
     // If the original URL can't be found, leave it empty.
     std::string original_request_url_spec;
@@ -333,12 +323,6 @@ bool SerializedNavigationEntry::ReadFromPickle(base::PickleIterator* iterator) {
     if (iterator->ReadInt(&correct_referrer_policy)) {
       referrer_policy_ = correct_referrer_policy;
     } else {
-      int mapped_referrer_policy;
-      if (!SerializedNavigationDriver::Get()->MapReferrerPolicyToNewValues(
-              referrer_policy_, &mapped_referrer_policy)) {
-        referrer_url_ = GURL();
-      }
-      referrer_policy_ = mapped_referrer_policy;
       encoded_page_state_ =
           SerializedNavigationDriver::Get()->StripReferrerFromPageState(
               encoded_page_state_);
@@ -368,14 +352,7 @@ bool SerializedNavigationEntry::ReadFromPickle(base::PickleIterator* iterator) {
 sync_pb::TabNavigation SerializedNavigationEntry::ToSyncData() const {
   sync_pb::TabNavigation sync_data;
   sync_data.set_virtual_url(virtual_url_.spec());
-  int mapped_referrer_policy;
-  if (SerializedNavigationDriver::Get()->MapReferrerPolicyToOldValues(
-          referrer_policy_, &mapped_referrer_policy)) {
-    sync_data.set_referrer(referrer_url_.spec());
-  } else {
-    sync_data.set_referrer(std::string());
-  }
-  sync_data.set_obsolete_referrer_policy(mapped_referrer_policy);
+  sync_data.set_referrer(referrer_url_.spec());
   sync_data.set_correct_referrer_policy(referrer_policy_);
   sync_data.set_title(base::UTF16ToUTF8(title_));