[Media Router] Clean up issues related code.

chrome/browser/media/router/issues_observer.cc

Index: chrome/browser/media/router/issues_observer.cc
diff --git a/chrome/browser/media/router/issues_observer.cc b/chrome/browser/media/router/issues_observer.cc
index 1590b0cda5ac05f8f3f462ab8a401a73b5d4597a..decdbe488e68a5e0195a89b7247a16d7b97dc940 100644
--- a/chrome/browser/media/router/issues_observer.cc
+++ b/chrome/browser/media/router/issues_observer.cc
@@ -9,19 +9,22 @@
 
 namespace media_router {
 
-IssuesObserver::IssuesObserver(MediaRouter* router) : router_(router) {
+IssuesObserver::IssuesObserver(MediaRouter* router)
+    : router_(router), initialized_(false) {
   DCHECK(router_);
 }
 
 IssuesObserver::~IssuesObserver() {
+  if (initialized_)
+    router_->UnregisterIssuesObserver(this);
 }
 
-void IssuesObserver::RegisterObserver() {
-  router_->RegisterIssuesObserver(this);
-}
+void IssuesObserver::Init() {
+  if (initialized_)
+    return;
 
-void IssuesObserver::UnregisterObserver() {
-  router_->UnregisterIssuesObserver(this);
+  router_->RegisterIssuesObserver(this);
+  initialized_ = true;

[dcheng, 2016/12/07 18:58:02]

Can you help me understand why this isn't just part of the constructor? Doing so
would remove the need for |initialized_| completely.

[imcheng, 2016/12/09 23:19:53]

RegisterIssuesObserver will synchronously invoke OnIssue() if there is currently
an issue, which is a virtual method -- this results in undefined behavior. Also
doing work in constructors is discouraged by style guideline.

 }
 
 }  // namespace media_router