Fix memory leak in ThreadWatcher.

chrome/browser/metrics/thread_watcher.h

Index: chrome/browser/metrics/thread_watcher.h
diff --git a/chrome/browser/metrics/thread_watcher.h b/chrome/browser/metrics/thread_watcher.h
index 6bf8d15cd1fccf0abf0abe431b6906861587f506..4ed6aa26ac1b15dc546383623f0eb180666c77f5 100644
--- a/chrome/browser/metrics/thread_watcher.h
+++ b/chrome/browser/metrics/thread_watcher.h
@@ -138,14 +138,14 @@ class ThreadWatcher {
   // Returns |ping_sequence_number_| (used by unit tests).
   uint64_t ping_sequence_number() const { return ping_sequence_number_; }
 
+  virtual ~ThreadWatcher();

[Ilya Sherman, 2016/08/31 03:54:42]

nit: Please move this to the top of the class definition:
https://google.github.io/styleguide/cppguide.html#Declaration_Order

[Joshua LeVasseur, 2016/08/31 19:06:50]

Done.

+
  protected:
   // Construct a ThreadWatcher for the given |thread_id|. |sleep_time| is the
   // wait time between ping messages. |unresponsive_time| is the wait time after
   // ping message is sent, to check if we have received pong message or not.
   explicit ThreadWatcher(const WatchingParams& params);
 
-  virtual ~ThreadWatcher();
-
   // This method activates the thread watching which starts ping/pong messaging.
   virtual void ActivateThreadWatching();
 
@@ -394,10 +394,9 @@ class ThreadWatcherList {
   static void StopWatchingAll();
 
   // Register() stores a pointer to the given ThreadWatcher in a global map.
-  static void Register(ThreadWatcher* watcher);
-
-  // This method returns true if the ThreadWatcher object is registerd.
-  static bool IsRegistered(const content::BrowserThread::ID thread_id);
+  // It takes ownership of the ThreadWatcher.  Returns true if it was

[Ilya Sherman, 2016/08/31 03:54:42]

nit: No need to document the ownership transfer -- that's clear just from the
use of unique_ptr.

[Joshua LeVasseur, 2016/08/31 19:06:50]

Done.

+  // successfully registered.
+  static bool Register(std::unique_ptr<ThreadWatcher> watcher);
 
   // This method returns number of responsive and unresponsive watched threads.
   static void GetStatusOfThreads(uint32_t* responding_thread_count,