Make PointerEvent fromElement/toElement return null.

Also added web-platform-tests.

Blink intent thread:
https://groups.google.com/a/chromium.org/forum/#!topic/blink-dev/G2s1Ol3qcgA

Closes https://github.com/w3c/pointerevents/issues/167

Bug: 827271
Change-Id: I8429b9541f8cfc38223b3a34116b74c2aba92ee5
Reviewed-on: https://chromium-review.googlesource.com/986877Reviewed-by: Dave Tapuska <dtapuska@chromium.org>
Commit-Queue: Mustaq Ahmed <mustaq@chromium.org>
Cr-Commit-Position: refs/heads/master@{#550683}

third_party/WebKit/LayoutTests/external/wpt/pointerevents/pointerevent_support.js

@@ -39,7 +39,8 @@ function check_PointerEvent(event, testNamePrefix) {
         "long": function (v) { return typeof v === "number" && Math.round(v) === v; },
         "float": function (v) { return typeof v === "number"; },
         "string": function (v) { return typeof v === "string"; },
-        "boolean": function (v) { return typeof v === "boolean" }
+        "boolean": function (v) { return typeof v === "boolean" },
+        "object": function (v) { return typeof v === "object" }
     };
     [
         ["readonly", "long", "pointerId"],
@@ -50,7 +51,9 @@ function check_PointerEvent(event, testNamePrefix) {
         ["readonly", "long", "tiltY"],
         ["readonly", "string", "pointerType"],
         ["readonly", "boolean", "isPrimary"],
-        ["readonly", "long", "detail", 0]
+        ["readonly", "long", "detail", 0],
+        ["readonly", "object", "fromElement", null],
+        ["readonly", "object", "toElement", null]
     ].forEach(function (attr) {
         var readonly = attr[0];
         var type = attr[1];
@@ -75,7 +78,7 @@ function check_PointerEvent(event, testNamePrefix) {
         }, pointerTestName + "." + name + " IDL type " + type + " (JS type was " + typeof event[name] + ")");
 
         // value check if defined
-        if (value != undefined) {
+        if (value !== undefined) {
             test(function () {
                 assert_equals(event[name], value, name + " attribute value");
             }, pointerTestName + "." + name + " value is " + value + ".");

third_party/blink/renderer/core/events/mouse_event.h

@@ -105,8 +105,8 @@ class CORE_EXPORT MouseEvent : public UIEventWithKeyState {
   }
   const String& region() const { return region_; }
 
-  Node* toElement() const;
-  Node* fromElement() const;
+  virtual Node* toElement() const;
+  virtual Node* fromElement() const;
 
   virtual DataTransfer* getDataTransfer() const { return nullptr; }
 

third_party/blink/renderer/core/events/pointer_event.cc

@@ -104,6 +104,14 @@ void PointerEvent::ReceivedTarget() {
   MouseEvent::ReceivedTarget();
 }
 
+Node* PointerEvent::toElement() const {
+  return nullptr;
+}
+
+Node* PointerEvent::fromElement() const {
+  return nullptr;
+}
+
 HeapVector<Member<PointerEvent>> PointerEvent::getCoalescedEvents() {
   if (coalesced_events_targets_dirty_) {
     for (auto coalesced_event : coalesced_events_)

third_party/blink/renderer/core/events/pointer_event.h

@@ -50,6 +50,11 @@ class CORE_EXPORT PointerEvent final : public MouseEvent {
 
   void ReceivedTarget() override;
 
+  // Always return null for fromElement and toElement because these fields
+  // (inherited from MouseEvents) are non-standard.
+  Node* fromElement() const final;
+  Node* toElement() const final;
+
   HeapVector<Member<PointerEvent>> getCoalescedEvents();
 
   DispatchEventResult DispatchEvent(EventDispatcher&) override;