Bug 1504911 - part 1: Make all "input" event dispatcher in C++ use new utility method r=smaug

Currently, a lot of code dispatch "input" event and some of them dispatch
"input" event with wrong interface and/or values.  Therefore this patch
creates nsContentUtils::DispatchInputEvent() to make all of them dispatch
correct event.

Unfortunately, due to bug 1506439, we cannot set pointer to refcountable
classes of MOZ_CAN_RUN_SCRIPT method to nullptr.  Therefore, this patch
creates temporary RefPtr<TextEditor> a lot even though it makes damage to
the performance if it's in a hot path.

This patch makes eEditorInput event dispatched with
InternalEditorInputEvent when "input" event should be dispatched with
dom::InputEvent.  However, this patch uses WidgetEvent whose message is
eUnidentifiedEvent and setting WidgetEvent::mSpecifiedEventType to
nsGkAtoms::oninput when "input" event should be dispatched with
dom::Event because we need to keep that eEditorInput and
InternalEditorInputEvent are mapped each other.

Differential Revision: https://phabricator.services.mozilla.com/D12244

layout/forms/nsFileControlFrame.cpp

@@ -459,11 +459,11 @@ nsFileControlFrame::DnDListener::HandleEvent(Event* aEvent)
         inputElement->SetFiles(fileList, true);
       }
 
-      nsContentUtils::DispatchTrustedEvent(inputElement->OwnerDoc(),
-                                           static_cast<nsINode*>(inputElement),
-                                           NS_LITERAL_STRING("input"),
-                                           CanBubble::eYes,
-                                           Cancelable::eNo);
+      RefPtr<TextEditor> textEditor;
+      DebugOnly<nsresult> rvIgnored =
+        nsContentUtils::DispatchInputEvent(inputElement);
+      NS_WARNING_ASSERTION(NS_SUCCEEDED(rvIgnored),
+                           "Failed to dispatch input event");
       nsContentUtils::DispatchTrustedEvent(inputElement->OwnerDoc(),
                                            static_cast<nsINode*>(inputElement),
                                            NS_LITERAL_STRING("change"),