Add UMA histogram timers for ProcessManager and BackgroundContentsService startup.

These measure the time taken in response to ExtensionService ready signaling. These are the 2 heaviest observers of ready.

BUG=453073

Review URL: https://codereview.chromium.org/874643003

Cr-Commit-Position: refs/heads/master@{#315081}

chrome/browser/background/background_contents_service.cc

@@ -10,6 +10,7 @@
 #include "base/command_line.h"
 #include "base/compiler_specific.h"
 #include "base/message_loop/message_loop.h"
+#include "base/metrics/histogram_macros.h"
 #include "base/prefs/pref_service.h"
 #include "base/prefs/scoped_user_pref_update.h"
 #include "base/strings/string_util.h"
@@ -343,10 +344,13 @@ void BackgroundContentsService::Observe(
     const content::NotificationDetails& details) {
   switch (type) {
     case extensions::NOTIFICATION_EXTENSIONS_READY_DEPRECATED: {
+      const base::TimeTicks start_time = base::TimeTicks::Now();
       Profile* profile = content::Source<Profile>(source).ptr();
       LoadBackgroundContentsFromManifests(profile);
       LoadBackgroundContentsFromPrefs(profile);
       SendChangeNotification(profile);
+      UMA_HISTOGRAM_TIMES("Extensions.BackgroundContentsServiceStartupTime",
+                          base::TimeTicks::Now() - start_time);
       break;
     }
     case chrome::NOTIFICATION_BACKGROUND_CONTENTS_DELETED:

extensions/browser/process_manager.cc

@@ -9,7 +9,7 @@
 #include "base/lazy_instance.h"
 #include "base/logging.h"
 #include "base/message_loop/message_loop.h"
-#include "base/metrics/histogram.h"
+#include "base/metrics/histogram_macros.h"
 #include "base/stl_util.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/time/time.h"
@@ -757,7 +757,10 @@ void ProcessManager::Observe(int type,
     case extensions::NOTIFICATION_EXTENSIONS_READY_DEPRECATED: {
       // TODO(jamescook): Convert this to use ExtensionSystem::ready() instead
       // of a notification.
+      const base::TimeTicks start_time = base::TimeTicks::Now();
       MaybeCreateStartupBackgroundHosts();
+      UMA_HISTOGRAM_TIMES("Extensions.ProcessManagerStartupHostsTime",
+                          base::TimeTicks::Now() - start_time);
       break;
     }
 

tools/metrics/histograms/histograms.xml

@@ -7953,6 +7953,15 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   </summary>
 </histogram>
 
+<histogram name="Extensions.BackgroundContentsServiceStartupTime"
+    units="milliseconds">
+  <owner>yoz@chromium.org</owner>
+  <summary>
+    Time taken to load BackgroundContents for apps at startup when the extension
+    system notifies that it is ready.
+  </summary>
+</histogram>
+
 <histogram name="Extensions.BackgroundPageLoadTime" units="milliseconds">
   <owner>kalman@chromium.org</owner>
   <summary>The time for an extension's background page to load.</summary>
@@ -8999,6 +9008,15 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   </summary>
 </histogram>
 
+<histogram name="Extensions.ProcessManagerStartupHostsTime"
+    units="milliseconds">
+  <owner>yoz@chromium.org</owner>
+  <summary>
+    The time taken to start up persistent background pages for extensions in
+    ExtensionProcessManager when the extension system notifies that it is ready.
+  </summary>
+</histogram>
+
 <histogram name="Extensions.ResourceDirectoryTimestampQueryLatency"
     units="milliseconds">
   <owner>asargent@chromium.org</owner>