Update CSSOM SmoothScroll Web Platform Test

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

Index: third_party/WebKit/Source/core/dom/Element.idl
diff --git a/third_party/WebKit/Source/core/dom/Element.idl b/third_party/WebKit/Source/core/dom/Element.idl
index f642b455026e80b37cbe48f0996bc713172f60e2..09b59264fb97d535f6063e021657676d2f9c6dcb 100644
--- a/third_party/WebKit/Source/core/dom/Element.idl
+++ b/third_party/WebKit/Source/core/dom/Element.idl
@@ -95,7 +95,8 @@ interface Element : Node {
     ClientRectList getClientRects();
     ClientRect getBoundingClientRect();
 
-    void scrollIntoView(optional (ScrollIntoViewOptions or boolean)? arg);
+    void scrollIntoView();
+    void scrollIntoView((ScrollIntoViewOptions or boolean)? arg);

[foolip, 2017/06/15 08:38:04]

This argument should not be nullable.

[sunyunjia, 2017/06/15 18:00:26]

If I remove the "?", and pass in null or undefined, it would be parsed as an
empty ScrollIntoViewOptions, which has the default value of "center, center".
According to the spec however, if the argument is not specified, the destination
should be "start, nearest". Simon(the author) just submitted another
scrollIntoView
test(https://github.com/w3c/web-platform-tests/commit/1ca1e676dcd995ca693bebfb7c095a977830d89c)
today, and expects the destination to be "start, nearest" for "undefined"
testcase.

[foolip, 2017/06/15 19:41:53]

The "If arg is not specified" case in the spec would be when the method overload
with no arguments is selected. If you make the C++ "void scrollIntoView(bool
align_to_top = true)" have no argument, then you should be able to handle the
"no argument" case internally while keeping the IDL matching the spec. The
easiest way is probably to have the no-argument variant call into the 1-argument
one with a ScrollIntoViewOptionsOrBoolean instance that holds true.

     [RuntimeEnabled=CSSOMSmoothScroll, ImplementedAs=scrollTo] void scroll(optional ScrollToOptions options);
     [RuntimeEnabled=CSSOMSmoothScroll, ImplementedAs=scrollTo] void scroll(unrestricted double x, unrestricted double y);
     [RuntimeEnabled=CSSOMSmoothScroll] void scrollTo(optional ScrollToOptions options);