ppapi: Opt-in to receive synthetic mouse events for touch-events.

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 73e279d8d144c53abf6f8a6ec2f15e7a23d8f73a..496a0a68b313e01a31c23f54796a65552773db62 100644
--- a/ppapi/api/ppb_input_event.idl
+++ b/ppapi/api/ppb_input_event.idl
@@ -265,7 +265,12 @@ enum PP_InputEvent_Class {
    *
    * Request touch events only if you intend to handle them. If the browser
    * knows you do not need to handle touch events, it can handle them at a
-   * higher level and achieve higher performance.
+   * higher level and achieve higher performance. If the plugin does not
+   * register for touch-events, then it will receive synthetic mouse events that
+   * are generated from the touch events (e.g. mouse-down for touch-start,
+   * mouse-move for touch-move (with left-button down), and mouse-up for
+   * touch-end. If the plugin does register for touch events, then the synthetic
+   * mouse events are not created.
    */
   PP_INPUTEVENT_CLASS_TOUCH = 1 << 3,
 
@@ -306,6 +311,9 @@ interface PPB_InputEvent {
    * processed very quickly, may have a noticeable effect on the performance of
    * the page.
    *
+   * Note that synthetic mouse events will be generated from touch events if
+   * (and only if) the you do not request touch events.
+   *
    * When requesting input events through this function, the events will be
    * delivered and <i>not</i> bubbled to the page. This means that even if you
    * aren't interested in the message, no other parts of the page will get