Run Mutation Observer and Custom Element callbacks consistently at microtask checkpoint

Source/core/dom/Microtask.cpp

Index: Source/core/dom/Microtask.cpp
diff --git a/Source/modules/inputmethod/Composition.cpp b/Source/core/dom/Microtask.cpp
similarity index 77%
copy from Source/modules/inputmethod/Composition.cpp
copy to Source/core/dom/Microtask.cpp
index 870e8ea20fe6e84711b12b2bfde5f8791f2645b3..da7b4273365701162d292e6dd17c4b129c0ef9c4 100644
--- a/Source/modules/inputmethod/Composition.cpp
+++ b/Source/core/dom/Microtask.cpp
@@ -29,26 +29,21 @@
  */
 
 #include "config.h"
-#include "modules/inputmethod/Composition.h"
 
-#include "core/dom/Node.h"
-#include "core/dom/Range.h"
+#include "core/dom/Microtask.h"
 
-namespace WebCore {
+#include "core/dom/CustomElementRegistry.h"
+#include "core/dom/MutationObserver.h"
 
-Composition::~Composition()
-{
-}
+namespace WebCore {
 
-PassRefPtr<Composition> Composition::create(Node* text, Range* caret)
+void Microtask::performCheckpoint()
 {
-  return adoptRef(new Composition(text, caret));
+    CustomElementRegistry::deliverAllLifecycleCallbacks();
+    MutationObserver::deliverAllMutations();
+    ASSERT(!CustomElementRegistry::hasQueuedLifecycleCallbacks());
+    // FIXME: Remove this when https://www.w3.org/Bugs/Public/show_bug.cgi?id=21962 is fixed
+    CustomElementRegistry::abandonAllQueuedLifecycleCallbacks();
 }
 
-Composition::Composition(Node* text, Range* caret)
-    : m_text(text)
-    , m_caret(caret)
-{
 }
-
-} // namespace WebCore