[WebXR] Implement EventTarget for XRCoordinateSystem

The spec[1] states that XRCoordinateSystem inherits EventTarget.
This patch implements the inheritance.

[1]: https://immersive-web.github.io/webxr/#xrcoordinatesystem-interface

Bug: None
Change-Id: I509ff04c8bbe76a499655fa48a726ac10f444716
Reviewed-on: https://chromium-review.googlesource.com/1189503
Commit-Queue: Byoungkwon Ko <codeimpl@gmail.com>
Reviewed-by: Brandon Jones <bajones@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Cr-Commit-Position: refs/heads/master@{#592632}

third_party/WebKit/LayoutTests/external/wpt/webxr/idlharness.https.window-expected.txt

@@ -58,10 +58,10 @@ PASS XRFrame interface: attribute session
 PASS XRFrame interface: attribute views
 PASS XRFrame interface: operation getDevicePose(XRCoordinateSystem)
 PASS XRFrame interface: operation getInputPose(XRInputSource, XRCoordinateSystem)
-FAIL XRCoordinateSystem interface: existence and properties of interface object assert_equals: prototype of XRCoordinateSystem is not EventTarget expected function "function EventTarget() { [native code] }" but got function "function () { [native code] }"
+PASS XRCoordinateSystem interface: existence and properties of interface object
 PASS XRCoordinateSystem interface object length
 PASS XRCoordinateSystem interface object name
-FAIL XRCoordinateSystem interface: existence and properties of interface prototype object assert_equals: prototype of XRCoordinateSystem.prototype is not EventTarget.prototype expected object "[object EventTarget]" but got object "[object Object]"
+PASS XRCoordinateSystem interface: existence and properties of interface prototype object
 PASS XRCoordinateSystem interface: existence and properties of interface prototype object's "constructor" property
 PASS XRCoordinateSystem interface: existence and properties of interface prototype object's @@unscopables property
 PASS XRCoordinateSystem interface: operation getTransformTo(XRCoordinateSystem)

third_party/WebKit/LayoutTests/webexposed/global-interface-listing-expected.txt

@@ -10121,7 +10121,7 @@ interface XR : EventTarget
     method constructor
     method requestDevice
     setter ondevicechange
-interface XRCoordinateSystem
+interface XRCoordinateSystem : EventTarget
     attribute @@toStringTag
     method constructor
     method getTransformTo

third_party/blink/renderer/modules/event_target_modules_names.json5

@@ -57,6 +57,7 @@
     "modules/webmidi/MIDIInput",
     "modules/webmidi/MIDIPort",
     "modules/xr/XR",
+    "modules/xr/XRCoordinateSystem",
     "modules/xr/XRSession",
     {
       name: "modules/websockets/WebSocket",

third_party/blink/renderer/modules/xr/xr_coordinate_system.cc

@@ -4,6 +4,7 @@
 
 #include "third_party/blink/renderer/modules/xr/xr_coordinate_system.h"
 
+#include "third_party/blink/renderer/modules/event_target_modules.h"
 #include "third_party/blink/renderer/modules/xr/xr_session.h"
 
 namespace blink {
@@ -29,9 +30,18 @@ DOMFloat32Array* XRCoordinateSystem::getTransformTo(
   return nullptr;
 }
 
+ExecutionContext* XRCoordinateSystem::GetExecutionContext() const {
+  return session()->GetExecutionContext();
+}
+
+const AtomicString& XRCoordinateSystem::InterfaceName() const {
+  return EventTargetNames::XRCoordinateSystem;
+}
+
 void XRCoordinateSystem::Trace(blink::Visitor* visitor) {
   visitor->Trace(session_);
   ScriptWrappable::Trace(visitor);
+  EventTargetWithInlineData::Trace(visitor);
 }
 
 }  // namespace blink

third_party/blink/renderer/modules/xr/xr_coordinate_system.h

@@ -5,6 +5,7 @@
 #ifndef THIRD_PARTY_BLINK_RENDERER_MODULES_XR_XR_COORDINATE_SYSTEM_H_
 #define THIRD_PARTY_BLINK_RENDERER_MODULES_XR_XR_COORDINATE_SYSTEM_H_
 
+#include "third_party/blink/renderer/core/dom/events/event_target.h"
 #include "third_party/blink/renderer/core/typed_arrays/dom_typed_array.h"
 #include "third_party/blink/renderer/platform/bindings/script_wrappable.h"
 #include "third_party/blink/renderer/platform/heap/handle.h"
@@ -15,7 +16,7 @@ namespace blink {
 class TransformationMatrix;
 class XRSession;
 
-class XRCoordinateSystem : public ScriptWrappable {
+class XRCoordinateSystem : public EventTargetWithInlineData {
   DEFINE_WRAPPERTYPEINFO();
 
  public:
@@ -24,7 +25,11 @@ class XRCoordinateSystem : public ScriptWrappable {
 
   DOMFloat32Array* getTransformTo(XRCoordinateSystem*) const;
 
-  XRSession* session() { return session_; }
+  XRSession* session() const { return session_; }
+
+  // EventTarget overrides.
+  ExecutionContext* GetExecutionContext() const override;
+  const AtomicString& InterfaceName() const override;
 
   virtual std::unique_ptr<TransformationMatrix> TransformBasePose(
       const TransformationMatrix& base_pose) = 0;

third_party/blink/renderer/modules/xr/xr_coordinate_system.idl

@@ -7,6 +7,6 @@
     SecureContext,
     Exposed=Window,
     OriginTrialEnabled=WebXR
-] interface XRCoordinateSystem {
+] interface XRCoordinateSystem : EventTarget {
   Float32Array? getTransformTo(XRCoordinateSystem other);
 };