[Sessions] Add detailed logging of SessionRestore events.

content/public/browser/session_restore_uma.h

Index: content/public/browser/session_restore_uma.h
diff --git a/content/public/browser/session_restore_uma.h b/content/public/browser/session_restore_uma.h
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+++ b/content/public/browser/session_restore_uma.h
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+// Copyright 2015 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.
+//
+// UMA related constants for session restore experiments and metrics.
+
+#ifndef CONTENT_PUBLIC_BROWSER_SESSION_RESTORE_UMA_H_
+#define CONTENT_PUBLIC_BROWSER_SESSION_RESTORE_UMA_H_
+
+namespace content {
+
+// Field trials.
+
+// The name of the ongoing session restore field trial.
+extern const char kSessionRestoreBackgroundLoading[];
+
+// Metrics.
+
+// Name of the session restore actions histogram.
+extern const char kSessionRestoreActions[];
+
+// The name of the session restore tab actions metric.
+extern const char kSessionRestoreTabActions[];
+
+// Name of the histogram of the number of tabs implicated in a session
+// restore event.
+extern const char kSessionRestoreTabCount[];
+
+// Metric enums.
+
+// The enumeration values stored in the kSessionRestoreActions histogram.
+enum SessionRestoreActionsUma {
+  // Counts the total number of session restores that have occurred.
+  kSessionRestoreActionsUma_Initiated = 0,
+  // Counts the number of session restores that have been interrupted by
+  // memory pressure signals.
+  kSessionRestoreActionsUma_InterruptedByMemoryPressure = 1,
+  // The size of this enum. Must be the last entry.
+  kSessionRestoreActionsUma_Max,
+};
+
+// The enumeration of values stored in the kSessionRestoreTabActions histogram.
+enum SessionRestoreTabActionsUma {
+  // Incremented for each tab created in a session restore.
+  kSessionRestoreTabActionsUma_TabCreated = 0,
+  // Incremented for each foreground tab loaded by the session restore.
+  kSessionRestoreTabActionsUma_ForegroundTabLoaded = 1,
+  // Incremented for each background tab loaded by the session restore.
+  kSessionRestoreTabActionsUma_BackgroundTabLoaded = 2,
+  // Incremented for each tab that session restore decides not to load.
+  kSessionRestoreTabActionsUma_TabLoadingDeferred = 3,
+  // Incremented for each session restore deferred tab that is subsequently
+  // loaded by user action.
+  kSessionRestoreTabActionsUma_DeferredTabLoadedByUserAction = 4,
+  // The size of this enum. Must be the last entry.
+  kSessionRestoreTabActionsUma_Max,
+};
+
+}  // namespace content
+
+#endif  // CONTENT_PUBLIC_BROWSER_SESSION_RESTORE_UMA_H_