IDL: For DOMString? attribute getters, use null string to represent null

IDL: For DOMString? attribute getters, use null string to represent null

Same as we do for wrapper type attributes, where a null pointer is used
to represent a null Javascript value, use a null string (one for which
WTF::String::isNull() returns true) to represent a null Javascript value
for nullable DOMString attributes.

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=177221

[Jens Widell, 2014-06-30 10:43:41]

PTAL

I intend to follow-up with a CL that drops the if-null-return-null code for
nullable strings in favor of using v8SetReturnValueStringOrNull().

After that, we could drop uses of [TreatReturnedNullStringAs=Null] and just mark
the attribute as nullable instead, without CG changes.

https://codereview.chromium.org/338843005/diff/1/Source/bindings/tests/result...
File Source/bindings/tests/results/V8TestObject.cpp (right):

https://codereview.chromium.org/338843005/diff/1/Source/bindings/tests/result...
Source/bindings/tests/results/V8TestObject.cpp:1523: String
cppValue(impl->stringOrNullAttribute());
For reference, this change is identical to the change in CG for
NavigatorLanguage.language and MouseEventHitRegion.region. (And that's the only
way CG changes.)

[haraken, 2014-06-30 13:08:19]

LGTM!

[Jens Widell, 2014-06-30 13:34:33]

The CQ bit was checked by jl@opera.com

[commit-bot: I haz the power, 2014-06-30 13:34:50]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/jl@opera.com/338843005/1

[commit-bot: I haz the power, 2014-06-30 17:04:34]

Change committed as 177221