Eraser tool type plumbing from ui/events to web events and PPAPI.

ppapi/api/ppb_input_event.idl

Index: ppapi/api/ppb_input_event.idl
diff --git a/ppapi/api/ppb_input_event.idl b/ppapi/api/ppb_input_event.idl
index b9224fa584ad4e47ef060249fb0f80b3f67d72f4..d3fac5734d4d0768bf7067b3625d45ccd0234941 100644
--- a/ppapi/api/ppb_input_event.idl
+++ b/ppapi/api/ppb_input_event.idl
@@ -10,7 +10,8 @@
 label Chrome {
   M13 = 1.0,
   M14 = 1.1,
-  M34 = 1.2
+  M34 = 1.2,
+  M54 = 1.3

[bbudge, 2016/08/30 22:05:54]

This doesn't actually version the API

I'm going to reverse myself on this. To properly version this API would be
difficult, and the chance of this change breaking an existing app seems remote
(basically an app would have to be depending on these modifier bits being zero.)

A plugin that knows about these modifiers should run fine on older versions of
Chrome - it would just receive unmodified mouse events, which it should be able
to handle in any case. On versions of Chrome that do support these bits, the app
would be able to detect that and handle those modified events differently.

Since we don't really support versioning enum values (the code generator just
ignores those) you'd have to version the PPP_InputEvent interface, which is how
plugins receive events. Versioning PPP interfaces is more difficult. You would
have to modify a lot of Pepper code and check for API versions in the Pepper
proxy.

So this is fine as it is. It would probably be a good idea to annotate the new
values below with the version. See this CL which added a flag to the PPB_FileIO
API (which was technically a breaking change to a Stable API):

https://chromiumcodereview.appspot.com/16765005

[denniskempin, 2016/09/01 16:56:21]

There is one problem that I could see: 

Older versions of chrome do not filter the modifier flags. ISPEN and ISERASER
will be mapped to IsTouchAccessibility or IsComposing of
WebInputEvent::Modifiers. 

So running an app that uses the PEN/ERASER flags might break in weird ways in
older versions of chrome. Can the app query this input API version and disable
checking for the eraser flag? I have never used PPAPI myself. 

I will add the version flags to the enum values below. 

 };
 
 /**
@@ -199,7 +200,9 @@ enum PP_InputEvent_Modifier {
   PP_INPUTEVENT_MODIFIER_CAPSLOCKKEY      = 1 << 9,
   PP_INPUTEVENT_MODIFIER_NUMLOCKKEY       = 1 << 10,
   PP_INPUTEVENT_MODIFIER_ISLEFT           = 1 << 11,
-  PP_INPUTEVENT_MODIFIER_ISRIGHT          = 1 << 12
+  PP_INPUTEVENT_MODIFIER_ISRIGHT          = 1 << 12,
+  PP_INPUTEVENT_MODIFIER_ISPEN            = 1 << 13,
+  PP_INPUTEVENT_MODIFIER_ISERASER         = 1 << 14

[bbudge, 2016/08/30 22:05:54]

Annotate these both with [version=1.3] even though it's essentially a no-op.

[denniskempin, 2016/09/01 16:56:21]

Acknowledged.

 };
 
 /**