[Tab Metrics] Measure FP, FCP and FMP for Foreground Tab during Session Restore

chrome/browser/page_load_metrics/observers/session_restore_page_load_metrics_observer.cc

Index: chrome/browser/page_load_metrics/observers/session_restore_page_load_metrics_observer.cc
diff --git a/chrome/browser/page_load_metrics/observers/session_restore_page_load_metrics_observer.cc b/chrome/browser/page_load_metrics/observers/session_restore_page_load_metrics_observer.cc
new file mode 100644
index 0000000000000000000000000000000000000000..a1c5f8279e9f795cf19c545e980f2617cd64d917
--- /dev/null
+++ b/chrome/browser/page_load_metrics/observers/session_restore_page_load_metrics_observer.cc
@@ -0,0 +1,71 @@
+// Copyright 2017 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/page_load_metrics/observers/session_restore_page_load_metrics_observer.h"
+
+#include "base/metrics/histogram_macros.h"
+#include "chrome/browser/browser_process.h"
+
+namespace internal {
+
+const char kHistogramSessionRestoreForegroundTabFirstPaint[] =
+    "TabManager.Experimental.SessionRestore.ForegroundTab.FirstPaint";
+const char kHistogramSessionRestoreForegroundTabFirstContentfulPaint[] =
+    "TabManager.Experimental.SessionRestore.ForegroundTab.FirstContentfulPaint";
+const char kHistogramSessionRestoreForegroundTabFirstMeaningfulPaint[] =
+    "TabManager.Experimental.SessionRestore.ForegroundTab.FirstMeaningfulPaint";
+
+}  // namespace internal
+
+// static
+std::unique_ptr<SessionRestorePageLoadMetricsObserver>
+SessionRestorePageLoadMetricsObserver::CreateIfNeeded() {
+  resource_coordinator::TabManager* tab_manager =
+      g_browser_process->GetTabManager();
+  // This is used only on TabManager-supported platforms.
+  DCHECK(tab_manager);
+  return tab_manager->IsSessionRestoreLoadingTabs() &&
+                 !tab_manager->HasSessionRestoreInitialForegroundTabChanged()
+             ? base::MakeUnique<SessionRestorePageLoadMetricsObserver>()
+             : nullptr;
+}
+
+page_load_metrics::PageLoadMetricsObserver::ObservePolicy
+SessionRestorePageLoadMetricsObserver::OnStart(
+    content::NavigationHandle* navigation_handle,
+    const GURL& currently_committed_url,
+    bool started_in_foreground) {
+  return started_in_foreground ? CONTINUE_OBSERVING : STOP_OBSERVING;
+}
+
+page_load_metrics::PageLoadMetricsObserver::ObservePolicy
+SessionRestorePageLoadMetricsObserver::OnHidden(

[Bryan McQuade, 2017/06/30 20:04:38]

reading the comments in
https://cs.chromium.org/chromium/src/ui/base/page_transition_types.h, it sounds
like we can be even more confident that we're only measuring session restore
navs if we also check the PageTransition value of the navigation. I see:

  // SessionRestore and undo tab close use this transition type too.
  PAGE_TRANSITION_RELOAD = 8,

Given this, can we do something similar to
https://cs.chromium.org/chromium/src/chrome/browser/page_load_metrics/observe...,
where we get the transition type in OnCommit(), and return STOP_OBSERVING if a
navigation doesn't have the PAGE_TRANSITION_RELOAD transition type?

Something like:

// session restores use transition reload, so we only observe loads with a
reload transition type.
return ui::PageTransitionCoreTypeIs(transition, ui::PAGE_TRANSITION_RELOAD) ?
CONTINUE_OBSERVING : STOP_OBSERVING;

[ducbui, 2017/06/30 22:03:51]

Done. I agree that this condition will filter out new page loads in the initial
foreground tab during session restore.

+    const page_load_metrics::mojom::PageLoadTiming& timing,
+    const page_load_metrics::PageLoadExtraInfo& info) {
+  return STOP_OBSERVING;
+}
+
+void SessionRestorePageLoadMetricsObserver::OnFirstPaintInPage(
+    const page_load_metrics::mojom::PageLoadTiming& timing,
+    const page_load_metrics::PageLoadExtraInfo& extra_info) {
+  UMA_HISTOGRAM_TIMES(internal::kHistogramSessionRestoreForegroundTabFirstPaint,

[Bryan McQuade, 2017/06/30 20:04:38]

let's use PAGE_LOAD_HISTOGRAM rather than UMA_HISTOGRAM_TIMES to be consistent
with all other page load metrics observers (same for below)

[ducbui, 2017/06/30 22:03:51]

Done.

+                      timing.paint_timing->first_paint.value());
+}
+
+void SessionRestorePageLoadMetricsObserver::OnFirstContentfulPaintInPage(
+    const page_load_metrics::mojom::PageLoadTiming& timing,
+    const page_load_metrics::PageLoadExtraInfo& extra_info) {
+  UMA_HISTOGRAM_TIMES(
+      internal::kHistogramSessionRestoreForegroundTabFirstContentfulPaint,
+      timing.paint_timing->first_contentful_paint.value());
+}
+
+void SessionRestorePageLoadMetricsObserver::
+    OnFirstMeaningfulPaintInMainFrameDocument(
+        const page_load_metrics::mojom::PageLoadTiming& timing,
+        const page_load_metrics::PageLoadExtraInfo& extra_info) {
+  UMA_HISTOGRAM_TIMES(
+      internal::kHistogramSessionRestoreForegroundTabFirstMeaningfulPaint,
+      timing.paint_timing->first_meaningful_paint.value());
+}