Skip oversized logs when persisting logs instead of discarding them.

components/metrics/persisted_logs.cc

Index: components/metrics/persisted_logs.cc
diff --git a/components/metrics/persisted_logs.cc b/components/metrics/persisted_logs.cc
index 7213b59806131c66868b7f4f651e1c1bd151c106..f3cc5fdf679cf78d4d4cd683cdf5396897a6533d 100644
--- a/components/metrics/persisted_logs.cc
+++ b/components/metrics/persisted_logs.cc
@@ -86,7 +86,7 @@ PersistedLogs::PersistedLogs(PrefService* local_state,
       old_pref_name_(old_pref_name),
       min_log_count_(min_log_count),
       min_log_bytes_(min_log_bytes),
-      max_log_size_(max_log_size),
+      max_log_size_(max_log_size != 0 ? max_log_size : static_cast<size_t>(-1)),
       last_provisional_store_index_(-1) {
   DCHECK(local_state_);
   // One of the limit arguments must be non-zero.
@@ -95,22 +95,7 @@ PersistedLogs::PersistedLogs(PrefService* local_state,
 
 PersistedLogs::~PersistedLogs() {}
 
-void PersistedLogs::SerializeLogs() {
-  // Remove any logs that are over the serialization size limit.
-  if (max_log_size_) {
-    for (std::vector<LogHashPair>::iterator it = list_.begin();
-         it != list_.end();) {
-      size_t log_size = it->compressed_log_data.length();
-      if (log_size > max_log_size_) {
-        UMA_HISTOGRAM_COUNTS("UMA.Large Accumulated Log Not Persisted",
-                             static_cast<int>(log_size));
-        it = list_.erase(it);
-      } else {
-        ++it;
-      }
-    }
-  }
-
+void PersistedLogs::SerializeLogs() const {
   ListPrefUpdate update(local_state_, pref_name_);
   WriteLogsToPrefList(update.Get());
 
@@ -169,33 +154,35 @@ void PersistedLogs::DiscardLastProvisionalStore() {
   last_provisional_store_index_ = -1;
 }
 
-void PersistedLogs::WriteLogsToPrefList(base::ListValue* list_value) {
+void PersistedLogs::WriteLogsToPrefList(base::ListValue* list_value) const {
   list_value->Clear();
-  // Leave the list completely empty if there are no storable values.
-  if (list_.empty())
-    return;
 
-  size_t start = 0;
-  // If there are too many logs, keep the most recent logs up to the length
-  // limit, and at least to the minimum number of bytes.
-  if (list_.size() > min_log_count_) {
-    start = list_.size();
-    size_t bytes_used = 0;
-    std::vector<LogHashPair>::const_reverse_iterator end = list_.rend();
-    for (std::vector<LogHashPair>::const_reverse_iterator it = list_.rbegin();
-         it != end; ++it) {
-      const size_t log_size = it->compressed_log_data.length();
-      if (bytes_used >= min_log_bytes_ &&
-          (list_.size() - start) >= min_log_count_) {
-        break;
-      }
-      bytes_used += log_size;
-      --start;
+  // Keep the most recent logs which are smaller than |max_log_size_|.
+  // We keep at least |min_log_bytes_| and |min_log_count_| of logs before
+  // discarding older logs.
+  size_t start = list_.size();
+  size_t saved_log_count = 0;
+  size_t bytes_used = 0;
+  for (; start > 0; --start) {
+    size_t log_size = list_[start - 1].compressed_log_data.length();
+    if (bytes_used >= min_log_bytes_ &&
+        saved_log_count >= min_log_count_) {
+      break;
     }
+    // Oversized logs won't be persisted, so don't count them.
+    if (log_size > max_log_size_)
+      continue;
+    bytes_used += log_size;
+    ++saved_log_count;
   }
-  DCHECK_LT(start, list_.size());
 
   for (size_t i = start; i < list_.size(); ++i) {
+    size_t log_size = list_[i].compressed_log_data.length();
+    if (log_size > max_log_size_) {
+      UMA_HISTOGRAM_COUNTS("UMA.Large Accumulated Log Not Persisted",
+                           static_cast<int>(log_size));
+      continue;
+    }
     AppendBase64String(list_[i].compressed_log_data, list_value);
     AppendBase64String(list_[i].hash, list_value);
   }