Adding matrixTrasnform to DOMPointReadOnly interfaces as following spec.

third_party/WebKit/Source/core/dom/DOMPointReadOnly.idl

Index: third_party/WebKit/Source/core/dom/DOMPointReadOnly.idl
diff --git a/third_party/WebKit/Source/core/dom/DOMPointReadOnly.idl b/third_party/WebKit/Source/core/dom/DOMPointReadOnly.idl
index 15a44d47e635240f9c32239f032d8d0602f2cefc..ebfa10e428434627e782d223fcf8494cea854963 100644
--- a/third_party/WebKit/Source/core/dom/DOMPointReadOnly.idl
+++ b/third_party/WebKit/Source/core/dom/DOMPointReadOnly.idl
@@ -5,8 +5,8 @@
 // https://dev.w3.org/fxtf/geometry/#DOMPoint
 
 [
-    Constructor(unrestricted double x, unrestricted double y,
-                unrestricted double z, unrestricted double w),
+    Constructor(optional unrestricted double x = 0, optional unrestricted double y = 0,

[zino, 2017/01/03 16:16:55]

Please add some tests for this change?

[Byoungkwon Ko, 2017/01/03 16:35:39]

Done.

+                optional unrestricted double z = 0, optional unrestricted double w = 1),
     // FIXME: Exposed=(Window,Worker)
     RuntimeEnabled=GeometryInterfaces,
 ] interface DOMPointReadOnly {
@@ -20,4 +20,5 @@
     // FIXME: Implement matrixTransform.
     // DOMPoint matrixTransform(DOMMatrixReadOnly matrix);
     serializer = { attribute };
+    [RaisesException] DOMPoint matrixTransform(optional DOMMatrixInit matrix);
 };