Add a "Keepalive count" column to Task Manager.

chrome/browser/task_manager/providers/task.h

Index: chrome/browser/task_manager/providers/task.h
diff --git a/chrome/browser/task_manager/providers/task.h b/chrome/browser/task_manager/providers/task.h
index 0c04857e9846969a495f6cbfe7ba011115bbd941..d112d38f8ddd31d5bf580d1965d977a544302e5b 100644
--- a/chrome/browser/task_manager/providers/task.h
+++ b/chrome/browser/task_manager/providers/task.h
@@ -135,6 +135,9 @@ class Task {
   virtual bool ReportsWebCacheStats() const;
   virtual blink::WebCache::ResourceTypeStats GetWebCacheStats() const;
 
+  // Returns the keep-alive counter if the Task is an event page, -1 otherwise.
+  virtual int GetKeepaliveCount() const;
+
   // Checking whether the task reports network usage.
   bool ReportsNetworkUsage() const;