[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..c285d6c06fef30803e959fa2251e9836b079ba68
--- /dev/null
+++ b/chrome/browser/page_load_metrics/observers/session_restore_page_load_metrics_observer.cc
@@ -0,0 +1,79 @@
+// 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/logging.h"
+#include "chrome/browser/browser_process.h"
+#include "chrome/browser/page_load_metrics/page_load_metrics_util.h"
+#include "chrome/browser/resource_coordinator/tab_manager.h"
+#include "chrome/common/page_load_metrics/page_load_metrics.mojom.h"
+#include "content/public/browser/navigation_handle.h"
+#include "content/public/browser/web_contents.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
+
+SessionRestorePageLoadMetricsObserver::SessionRestorePageLoadMetricsObserver() {
+}
+
+page_load_metrics::PageLoadMetricsObserver::ObservePolicy
+SessionRestorePageLoadMetricsObserver::OnStart(
+    content::NavigationHandle* navigation_handle,
+    const GURL& currently_committed_url,
+    bool started_in_foreground) {
+  content::WebContents* contents = navigation_handle->GetWebContents();
+  resource_coordinator::TabManager* tab_manager =
+      g_browser_process->GetTabManager();
+  // Should not be null because this is used only on supported platforms.
+  DCHECK(tab_manager);
+
+  return (started_in_foreground &&

[Bryan McQuade, 2017/08/12 14:10:36]

just noticed - any reason we stopped testing for RELOAD transition type and/or a
valid restore type? seems like that would only serve to make the metric more
accurate.

[ducbui, 2017/08/13 23:56:43]

I think the test may be redundant because a tab is set to be in session restore
only in OnWillRestoreTab() whose execution implies that the transition type is
RELOAD and the restore type is from last session.

I put some DCHECKs to test RELOAD transition and valid restore types; the
DCHECKs have no failure in tests
(https://chromium-review.googlesource.com/c/612592). Therefore, I believe 
that current filtering conditions may fail only in very corner cases.

I will change the DCHECKs to the conditions in the observer if you think they
are necessary.

+          tab_manager->IsTabInSessionRestore(contents) &&
+          tab_manager->IsTabRestoredInForeground(contents))
+             ? CONTINUE_OBSERVING
+             : STOP_OBSERVING;
+}
+
+void SessionRestorePageLoadMetricsObserver::OnFirstPaintInPage(
+    const page_load_metrics::mojom::PageLoadTiming& timing,
+    const page_load_metrics::PageLoadExtraInfo& extra_info) {
+  if (page_load_metrics::WasStartedInForegroundOptionalEventInForeground(
+          timing.paint_timing->first_paint.value(), extra_info)) {
+    PAGE_LOAD_HISTOGRAM(
+        internal::kHistogramSessionRestoreForegroundTabFirstPaint,
+        timing.paint_timing->first_paint.value());
+  }
+}
+
+void SessionRestorePageLoadMetricsObserver::OnFirstContentfulPaintInPage(
+    const page_load_metrics::mojom::PageLoadTiming& timing,
+    const page_load_metrics::PageLoadExtraInfo& extra_info) {
+  if (page_load_metrics::WasStartedInForegroundOptionalEventInForeground(
+          timing.paint_timing->first_contentful_paint.value(), extra_info)) {
+    PAGE_LOAD_HISTOGRAM(
+        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) {
+  if (page_load_metrics::WasStartedInForegroundOptionalEventInForeground(
+          timing.paint_timing->first_meaningful_paint.value(), extra_info)) {
+    PAGE_LOAD_HISTOGRAM(
+        internal::kHistogramSessionRestoreForegroundTabFirstMeaningfulPaint,
+        timing.paint_timing->first_meaningful_paint.value());
+  }
+}