Cache pointers to histograms for recording event times.

ui/events/event.cc

 // Copyright (c) 2012 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 "ui/events/event.h"
 
 #include <utility>
 
 #if defined(USE_X11)
 #include <X11/extensions/XInput2.h>
@@ skipping 294 matching lines @@
       phase_(EP_PREDISPATCH),
       result_(ER_UNHANDLED),
       source_device_id_(ED_UNKNOWN_DEVICE) {
   base::TimeDelta delta = EventTimeForNow() - time_stamp_;
   if (type_ < ET_LAST)
     name_ = EventTypeName(type_);
   base::HistogramBase::Sample delta_sample =
       static_cast<base::HistogramBase::Sample>(delta.InMicroseconds());
   UMA_HISTOGRAM_CUSTOM_COUNTS("Event.Latency.Browser", delta_sample, 1, 1000000,
                               100);
-  std::string name_for_event =
-      base::StringPrintf("Event.Latency.Browser.%s", name_.c_str());
-  base::HistogramBase* counter_for_type =
+
+  // Though it seems inefficient to generate the string twice, the first
+  // instance will be used only for DCHECK builds and the second won't be
+  // executed at all if the histogram was previously accessed here.
+  STATIC_HISTOGRAM_POINTER_GROUP(
+      base::StringPrintf("Event.Latency.Browser.%s", name_.c_str()),
+      type_, ET_LAST, Add(delta_sample),
       base::Histogram::FactoryGet(
-          name_for_event,
-          1,
-          1000000,
-          100,
-          base::HistogramBase::kUmaTargetedHistogramFlag);
-  counter_for_type->Add(delta_sample);
+          base::StringPrintf("Event.Latency.Browser.%s", name_.c_str()),
+          1, 1000000, 100,
+          base::HistogramBase::kUmaTargetedHistogramFlag));
 
 #if defined(USE_X11)
   if (native_event->type == GenericEvent) {
     XIDeviceEvent* xiev =
         static_cast<XIDeviceEvent*>(native_event->xcookie.data);
     source_device_id_ = xiev->sourceid;
   }
 #endif
 #if defined(USE_OZONE)
   source_device_id_ =
@@ skipping 812 matching lines @@
                    gfx::PointF(x, y),
                    time_stamp,
                    flags | EF_FROM_TOUCH),
       details_(details) {
 }
 
 GestureEvent::~GestureEvent() {
 }
 
 }  // namespace ui