Remove all but one use of WeakPtrFactory::DetachFromThread.

remoting/host/policy_hack/policy_watcher_linux.cc

Index: remoting/host/policy_hack/policy_watcher_linux.cc
diff --git a/remoting/host/policy_hack/policy_watcher_linux.cc b/remoting/host/policy_hack/policy_watcher_linux.cc
index 641af9c065cdc07a17450cbb5ae2e3dcd19b992b..f3cffeafb0f0f7a050b8bb1f3085f7d6f4ff0434 100644
--- a/remoting/host/policy_hack/policy_watcher_linux.cc
+++ b/remoting/host/policy_hack/policy_watcher_linux.cc
@@ -51,12 +51,6 @@ class PolicyWatcherLinux : public PolicyWatcher {
       : PolicyWatcher(task_runner),
         config_dir_(config_dir),
         weak_factory_(this) {
-    // Detach the factory because we ensure that only the policy thread ever
-    // calls methods on this. Also, the API contract of having to call
-    // StopWatching() (which signals completion) after StartWatching()
-    // before this object can be destructed ensures there are no users of
-    // this object before it is destructed.
-    weak_factory_.DetachFromThread();
   }
 
   virtual ~PolicyWatcherLinux() {}
@@ -84,8 +78,12 @@ class PolicyWatcherLinux : public PolicyWatcher {
 
   virtual void StopWatchingInternal() OVERRIDE {
     DCHECK(OnPolicyWatcherThread());
-    // Cancel any inflight requests.
+
+    // Stop watching for changes to files in the policies directory.
     watcher_.reset();
+
+    // Orphan any pending OnFilePathChanged tasks.
+    weak_factory_.InvalidateWeakPtrs();
   }
 
  private: