Add UMA stats for discarded tabs on a per logged in user base

Each discarded tab will be "stored" in the bucket for the number of users logged in at the time of the occurrence. 
To get to a useful number, the value needs to be normalized by dividing the absolute value per bucket by the corresponding UsersPerSession bucket (in percent).

BUG=321739
TEST=visual

Review URL: https://codereview.chromium.org/104713003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@239023 0039d316-1c4b-4281-b951-d872f2087c98

4 files changed, 28 insertions, 0 deletions

diff --git a/ash/multi_profile_uma.cc b/ash/multi_profile_uma.cc
index ec29a83..cbf3b05 100644
--- a/ash/multi_profile_uma.cc
+++ b/ash/multi_profile_uma.cc
@@ -48,4 +48,10 @@ void MultiProfileUMA::RecordUserCount(int number_of_users) {
   UMA_HISTOGRAM_COUNTS_100("MultiProfile.UsersPerSession", number_of_users);
 }
 
+// static
+void MultiProfileUMA::RecordDiscardedTab(int number_of_users) {
+  UMA_HISTOGRAM_COUNTS_100("MultiProfile.DiscardedTabsPerUser",
+      number_of_users);
+}
+
 }  // namespace ash
diff --git a/ash/multi_profile_uma.h b/ash/multi_profile_uma.h
index e0b411f..937b4d81 100644
--- a/ash/multi_profile_uma.h
+++ b/ash/multi_profile_uma.h
@@ -72,6 +72,9 @@ class ASH_EXPORT MultiProfileUMA {
   // Record number of users joined into a session. Called upon logout.
   static void RecordUserCount(int number_of_users);
 
+  // Record a discarded tab in the number of running users bucket.
+  static void RecordDiscardedTab(int number_of_users);
+
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(MultiProfileUMA);
 };
diff --git a/chrome/browser/chromeos/memory/oom_priority_manager.cc b/chrome/browser/chromeos/memory/oom_priority_manager.cc
index 6de6c82..c8d9538 100644
--- a/chrome/browser/chromeos/memory/oom_priority_manager.cc
+++ b/chrome/browser/chromeos/memory/oom_priority_manager.cc
@@ -8,6 +8,9 @@
 #include <set>
 #include <vector>
 
+#include "ash/multi_profile_uma.h"
+#include "ash/session_state_delegate.h"
+#include "ash/shell.h"
 #include "base/bind.h"
 #include "base/bind_helpers.h"
 #include "base/command_line.h"
@@ -321,6 +324,12 @@ void OomPriorityManager::RecordDiscardStatistics() {
   UMA_HISTOGRAM_CUSTOM_COUNTS(
       "Tabs.Discard.TabCount", GetTabCount(), 1, 100, 50);
 
+  // Record the discarded tab in relation to the amount of simultaneously
+  // logged in users.
+  ash::MultiProfileUMA::RecordDiscardedTab(
+      ash::Shell::GetInstance()->session_state_delegate()->
+          NumberOfLoggedInUsers());
+
   // TODO(jamescook): If the time stats prove too noisy, then divide up users
   // based on how heavily they use Chrome using tab count as a proxy.
   // Bin into <= 1, <= 2, <= 4, <= 8, etc.
diff --git a/tools/metrics/histograms/histograms.xml b/tools/metrics/histograms/histograms.xml
index 133dc95..a3d0bd7 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -7222,6 +7222,16 @@ other types of suffix sets.
   </summary>
 </histogram>
 
+<histogram name="MultiProfile.DiscardedTabsPerUser">
+  <summary>
+    The relation of discarded tabs vs. the amount of simultaneous users. The
+    counts are the number of discards and the buckets are the number of users.
+    Since the count values are absolute numbers, they need to be normalized
+    before use - so divide the counts by the percentage of users found under
+    'MultiProfile.UsersPerSession'.
+  </summary>
+</histogram>
+
 <histogram name="MultiProfile.SessionMode" enum="MultiProfileSessionMode">
   <summary>
     The session counter for different multi profile modes which gets stored once