Add startup metrics that measure the performance of the first web contents.

chrome/browser/metrics/first_web_contents_profiler.cc

+// Copyright 2014 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 "chrome/browser/metrics/first_web_contents_profiler.h"
+
+#include "base/metrics/histogram.h"
+#include "base/process/process_info.h"
+#include "base/time/time.h"
+#include "chrome/browser/ui/browser.h"
+#include "chrome/browser/ui/browser_iterator.h"
+#include "chrome/browser/ui/tabs/tab_strip_model.h"
+
+namespace {

[Ilya Sherman, 2014/11/26 04:12:26]

nit: Please leave a blank line after this one.

[erikchen, 2014/11/26 18:24:43]

Done.

+const int kHistogramMinTimeMilliseconds = 200;
+const int kHistogramMaxTimeSeconds = 45;
+
+// The buckets need to be sufficiently tight that small performance
+// improvements can be measured. We want to be able to differentiate 1%
+// improvements, which requires 781 buckets.

[Ilya Sherman, 2014/11/26 04:12:26]

1% improvements to what?  Histograms measure a precise mean, so the number of
buckets is irrelevant for measuring improvements to the mean.  If you're not
tracking the mean, then what are you tracking?

[erikchen, 2014/11/26 18:24:43]

I'm tracking the two modes of a bi-modal distribution. I've significantly
expanded the documentation in patch set 3, so take a look at that for a more
detailed explanation.

+//    log(45 * 1000 / 200) / log (2) / 0.01 = 781.

[Ilya Sherman, 2014/11/26 04:12:26]

nit: I expect we'll arrive at some different computation; but if you find
yourself keeping this one, please just use "lg" in place of "log", and remove
the "/ log (2)" part.

[Ilya Sherman, 2014/11/26 04:12:26]

Sorry, but I don't understand the relevance of this computation.  Could you
please clarify why dividing the distance, in log space, by 0.01 gives an
interesting number?

[erikchen, 2014/11/26 18:24:43]

I've updated the explanation in patch set 3 to break down the computation into
documented subcomponents.

[erikchen, 2014/11/26 18:24:43]

Done.

+const int kHistogramBucketSize = 781;

[Ilya Sherman, 2014/11/26 04:12:26]

nit: Please leave a blank line after this one.

[erikchen, 2014/11/26 18:24:43]

Done.

+}  // namespace
+
+scoped_ptr<FirstWebContentsProfiler>
+FirstWebContentsProfiler::CreateProfilerForFirstWebContents(
+    FirstWebContentsProfilerDelegate* delegate) {
+  DCHECK(delegate);
+  for (chrome::BrowserIterator iterator; !iterator.done(); iterator.Next()) {
+    Browser* browser = *iterator;
+    content::WebContents* web_contents =
+        browser->tab_strip_model()->GetActiveWebContents();
+    if (web_contents) {
+      return scoped_ptr<FirstWebContentsProfiler>(
+          new FirstWebContentsProfiler(web_contents, delegate));
+    }
+  }
+  return nullptr;
+}
+
+FirstWebContentsProfiler::FirstWebContentsProfiler(
+    content::WebContents* web_contents,
+    FirstWebContentsProfilerDelegate* delegate)
+    : content::WebContentsObserver(web_contents),
+      collected_paint_metric_(false),
+      collected_load_metric_(false),
+      delegate_(delegate) {
+}
+
+void FirstWebContentsProfiler::DidFirstVisuallyNonEmptyPaint() {
+  if (collected_paint_metric_)
+    return;
+  collected_paint_metric_ = true;
+  const base::Time process_creation_time =
+      base::CurrentProcessInfo::CreationTime();
+  if (!process_creation_time.is_null()) {
+    base::TimeDelta elapsed = base::Time::Now() - process_creation_time;
+    UMA_HISTOGRAM_CUSTOM_TIMES(
+        "Startup.FirstWebContents.NonEmptyPaint", elapsed,
+        base::TimeDelta::FromMilliseconds(kHistogramMinTimeMilliseconds),
+        base::TimeDelta::FromSeconds(kHistogramMaxTimeSeconds),
+        kHistogramBucketSize);
+  }
+
+  if (IsFinishedCollectingMetrics())
+    FinishedCollectingMetrics();
+}
+
+void FirstWebContentsProfiler::DocumentOnLoadCompletedInMainFrame() {
+  if (collected_load_metric_)
+    return;
+  collected_load_metric_ = true;
+  const base::Time process_creation_time =
+      base::CurrentProcessInfo::CreationTime();
+  if (!process_creation_time.is_null()) {
+    base::TimeDelta elapsed = base::Time::Now() - process_creation_time;
+    UMA_HISTOGRAM_CUSTOM_TIMES(
+        "Startup.FirstWebContents.MainFrameLoad", elapsed,
+        base::TimeDelta::FromMilliseconds(kHistogramMinTimeMilliseconds),
+        base::TimeDelta::FromSeconds(kHistogramMaxTimeSeconds),
+        kHistogramBucketSize);
+  }
+
+  if (IsFinishedCollectingMetrics())
+    FinishedCollectingMetrics();
+}
+
+void FirstWebContentsProfiler::WebContentsDestroyed() {
+  FinishedCollectingMetrics();
+}
+
+bool FirstWebContentsProfiler::IsFinishedCollectingMetrics() {
+  return collected_paint_metric_ && collected_load_metric_;
+}
+
+void FirstWebContentsProfiler::FinishedCollectingMetrics() {
+  delegate_->ProfilerFinishedCollectingMetrics();
+}