Bug 1612724 - Part 1: Add a NotifyWhenScriptSafe helper method to nsIObserverService, r=froydnj

Differential Revision: https://phabricator.services.mozilla.com/D61600

--HG--
extra : moz-landing-system : lando

xpcom/ds/nsIObserverService.idl

@@ -63,6 +63,24 @@ interface nsIObserverService : nsISupports
                           in string aTopic,
                           [optional] in wstring someData );
 
+    %{C++
+    /**
+     * notifyWhenScriptSafe
+     *
+     * Notifies all registered listeners of the given topic once it is safe to
+     * run script.
+     *
+     * Implemented in "nsObserverService.cpp".
+     *
+     * @param aSubject : Notification specific interface pointer.
+     * @param aTopic   : The notification topic or subject.
+     * @param someData : Notification specific wide string.
+     */
+    nsresult NotifyWhenScriptSafe(nsISupports* aSubject,
+                                  const char* aTopic,
+                                  const char16_t* aData = nullptr);
+    %}
+
     /**
      * enumerateObservers
      *

xpcom/ds/nsObserverService.cpp

@@ -6,6 +6,7 @@
 
 #include "mozilla/Logging.h"
 #include "nsComponentManagerUtils.h"
+#include "nsContentUtils.h"
 #include "nsIConsoleService.h"
 #include "nsIObserverService.h"
 #include "nsIObserver.h"
@@ -318,3 +319,46 @@ nsObserverService::UnmarkGrayStrongObservers() {
 
   return NS_OK;
 }
+
+namespace {
+
+class NotifyWhenScriptSafeRunnable : public mozilla::Runnable {
+ public:
+  NotifyWhenScriptSafeRunnable(nsIObserverService* aObs, nsISupports* aSubject,
+                               const char* aTopic, const char16_t* aData)
+      : mozilla::Runnable("NotifyWhenScriptSafeRunnable"),
+        mObs(aObs),
+        mSubject(aSubject),
+        mTopic(aTopic) {
+    if (aData) {
+      mData.Assign(aData);
+    } else {
+      mData.SetIsVoid(true);
+    }
+  }
+
+  NS_IMETHOD Run() {
+    const char16_t* data = mData.IsVoid() ? nullptr : mData.get();
+    return mObs->NotifyObservers(mSubject, mTopic.get(), data);
+  }
+
+ private:
+  nsCOMPtr<nsIObserverService> mObs;
+  nsCOMPtr<nsISupports> mSubject;
+  nsCString mTopic;
+  nsString mData;
+};
+
+}  // namespace
+
+nsresult nsIObserverService::NotifyWhenScriptSafe(nsISupports* aSubject,
+                                                  const char* aTopic,
+                                                  const char16_t* aData) {
+  if (nsContentUtils::IsSafeToRunScript()) {
+    return NotifyObservers(aSubject, aTopic, aData);
+  }
+
+  nsContentUtils::AddScriptRunner(MakeAndAddRef<NotifyWhenScriptSafeRunnable>(
+      this, aSubject, aTopic, aData));
+  return NS_OK;
+}