Define DOM_KEY_LOCATION_* constants on KeyboardEvent

Source/core/dom/KeyboardEvent.idl

Index: Source/core/dom/KeyboardEvent.idl
diff --git a/Source/core/dom/KeyboardEvent.idl b/Source/core/dom/KeyboardEvent.idl
index cda219fa046a5e9267bf90a8bc30adc1e560042e..dd76eb9c838d15ff1305300a3eb0958a6e5ae8f5 100644
--- a/Source/core/dom/KeyboardEvent.idl
+++ b/Source/core/dom/KeyboardEvent.idl
@@ -21,6 +21,12 @@
 [
     ConstructorTemplate=Event
 ] interface KeyboardEvent : UIEvent {
+    const unsigned long DOM_KEY_LOCATION_STANDARD = 0x00;
+    const unsigned long DOM_KEY_LOCATION_LEFT     = 0x01;
+    const unsigned long DOM_KEY_LOCATION_RIGHT    = 0x02;
+    const unsigned long DOM_KEY_LOCATION_NUMPAD   = 0x03;
+    const unsigned long DOM_KEY_LOCATION_MOBILE   = 0x04;
+    const unsigned long DOM_KEY_LOCATION_JOYSTICK = 0x05;
 
     [InitializedByEventConstructor] readonly attribute DOMString        keyIdentifier;
     [InitializedByEventConstructor] readonly attribute unsigned long    keyLocation;

[Mike West, 2013/07/29 12:40:24]

This isn't really related to this CL, as it's existing behavior, but the spec
lists this as 'location' (no 'key' prefix). What do Gecko and IE do?

Relatedly, 'keyIdentifier' doesn't seem to be specified either, at least, not at
http://www.w3.org/TR/DOM-Level-3-Events/#events-keyboardevents.

[do-not-use, 2013/07/29 12:49:11]

I am already addressing this in:
https://codereview.chromium.org/20034002/

Both Gecko and IE10 support 'location'.