Bug 282266 - Populate imageClickedPoint when submitter is an image button. r=dom-core,layout-reviewers,emilio,masayuki

If the form submission originated from an event dispatch, this patch
ensures that the submitted image button coordinate is not the default.

Differential Revision: https://phabricator.services.mozilla.com/D224651

dom/html/HTMLInputElement.cpp

@@ -23,6 +23,7 @@
 #include "mozilla/dom/WindowContext.h"
 #include "mozilla/dom/InputType.h"
 #include "mozilla/dom/UserActivation.h"
+#include "mozilla/dom/MouseEvent.h"
 #include "mozilla/dom/MutationEventBinding.h"
 #include "mozilla/dom/WheelEventBinding.h"
 #include "mozilla/dom/WindowGlobalChild.h"
@@ -3353,6 +3354,18 @@ void HTMLInputElement::LegacyPreActivationBehavior(
     // latest one will be deferred until after the exit point of the
     // handler.
     mForm->OnSubmitClickBegin(this);
+
+    if (aVisitor.mDOMEvent) {
+      if (auto* mouseEvent = aVisitor.mDOMEvent->AsMouseEvent()) {
+        CSSIntPoint pt = mouseEvent->OffsetPoint();
+        if (auto* imageClickedPoint = static_cast<CSSIntPoint*>(
+                GetProperty(nsGkAtoms::imageClickedPoint))) {
+          // Ensures that a dispatched event's clicked point is not the default
+          // value.
+          *imageClickedPoint = pt;
+        }
+      }
+    }
   }
 }