Bug 1470545: Add chromeonly "shadowrootattached" event for devtools. r=smaug

Summary:

document.addEventListener("shadowrootattached", e => {
  // Do stuff with composedTarget.
});

I didn't bother to add tests for the event itself since this is going to get
tested in bug 1449333, but I can look into writing a chrome mochitest if you
want.

Test Plan: See above.

Reviewers: smaug

Bug #: 1470545

Differential Revision: https://phabricator.services.mozilla.com/D1777

MozReview-Commit-ID: 55cVMSsznMS

dom/base/Element.cpp

@@ -1263,6 +1263,17 @@ Element::AttachShadowWithoutNameChecks(ShadowRootMode aMode)
    */
   SetShadowRoot(shadowRoot);
 
+  // Dispatch a "shadowrootattached" event for devtools.
+  {
+    AsyncEventDispatcher* dispatcher =
+      new AsyncEventDispatcher(this,
+                               NS_LITERAL_STRING("shadowrootattached"),
+                               CanBubble::eYes,
+                               ChromeOnlyDispatch::eYes,
+                               Composed::eYes);
+    dispatcher->PostDOMEvent();
+  }
+
   /**
    * 6. Return shadow.
    */

dom/events/AsyncEventDispatcher.cpp

@@ -50,6 +50,7 @@ AsyncEventDispatcher::Run()
   }
   mTarget->AsyncEventRunning(this);
   if (mEventMessage != eUnidentifiedEvent) {
+    MOZ_ASSERT(mComposed == Composed::eDefault);
     return nsContentUtils::DispatchTrustedEvent<WidgetEvent>
       (node->OwnerDoc(), mTarget, mEventMessage, mCanBubble,
        Cancelable::eNo, nullptr /* aDefaultAction */, mOnlyChromeDispatch);
@@ -60,6 +61,10 @@ AsyncEventDispatcher::Run()
     event->InitEvent(mEventType, mCanBubble, Cancelable::eNo);
     event->SetTrusted(true);
   }
+  if (mComposed != Composed::eDefault) {
+    event->WidgetEventPtr()->mFlags.mComposed =
+      mComposed == Composed::eYes;
+  }
   if (mOnlyChromeDispatch == ChromeOnlyDispatch::eYes) {
     MOZ_ASSERT(event->IsTrusted());
     event->WidgetEventPtr()->mFlags.mOnlyChromeDispatch = true;

dom/events/AsyncEventDispatcher.h

@@ -39,13 +39,15 @@ public:
   AsyncEventDispatcher(nsINode* aTarget,
                        const nsAString& aEventType,
                        CanBubble aCanBubble,
-                       ChromeOnlyDispatch aOnlyChromeDispatch)
+                       ChromeOnlyDispatch aOnlyChromeDispatch,
+                       Composed aComposed = Composed::eDefault)
     : CancelableRunnable("AsyncEventDispatcher")
     , mTarget(aTarget)
     , mEventType(aEventType)
     , mEventMessage(eUnidentifiedEvent)
     , mCanBubble(aCanBubble)
     , mOnlyChromeDispatch(aOnlyChromeDispatch)
+    , mComposed(aComposed)
   {
   }
 
@@ -121,6 +123,7 @@ public:
   EventMessage          mEventMessage;
   CanBubble             mCanBubble = CanBubble::eNo;
   ChromeOnlyDispatch    mOnlyChromeDispatch = ChromeOnlyDispatch::eNo;
+  Composed              mComposed = Composed::eDefault;
   bool                  mCanceled = false;
   bool                  mCheckStillInDoc = false;
 };

widget/EventForwards.h

@@ -57,6 +57,13 @@ enum class Trusted
   eNo
 };
 
+enum class Composed
+{
+  eYes,
+  eNo,
+  eDefault
+};
+
 /**
  * Event messages
  */