Switch LatencyInfo struct to use a map.

cc/debug/latency_info.cc

+// Copyright (c) 2013 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 "cc/debug/latency_info.h"
+
+#include <algorithm>
+
+namespace cc {
+
+void LatencyInfo::MergeWith(const LatencyInfo& other) {
+  for (LatencyMap::const_iterator b = other.latency_components.begin();
+      b != other.latency_components.end(); ++b) {
+    AddLatencyNumberWithTimestamp(b->first.first, b->first.second,
+                                  b->second.sequence_number,
+                                  b->second.event_time,
+                                  b->second.event_count);
+  }
+}
+
+void LatencyInfo::AddLatencyNumber(LatencyComponentType component,
+                                   int64 id, int64 component_sequence_number) {
+  AddLatencyNumberWithTimestamp(component, id, component_sequence_number,
+                                base::TimeTicks::Now(), 1);
+}
+
+void LatencyInfo::AddLatencyNumberWithTimestamp(
+    LatencyComponentType component, int64 id, int64 component_sequence_number,
+    base::TimeTicks time, uint32_t event_count) {
+  LatencyMap::key_type key = std::make_pair(component, id);
+  LatencyMap::iterator f = latency_components.find(key);
+  if (f == latency_components.end()) {
+    LatencyComponent info = {component_sequence_number, time, event_count};
+    latency_components[key] = info;
+  } else {
+    f->second.sequence_number = std::max(component_sequence_number,
+                                         f->second.sequence_number);

[Chris Evans, 2013/04/17 00:54:59]

Nit: can avoid some minor duplication by declaring here,
uint32_t new_count = event_count + f->second.event_count;

and then using it in three places below.

+    if (event_count > 0 && event_count + f->second.event_count != 0) {
+      // Do a weighted average, so that the new event_time is the average of
+      // the times of events currently in this structure with the time passed
+      // into this method.
+      f->second.event_time += (time - f->second.event_time) * event_count /
+          (event_count + f->second.event_count);
+      f->second.event_count += event_count;
+    }
+  }
+}
+
+void LatencyInfo::Clear() {
+  latency_components.clear();
+}
+
+} // namespace cc
+