Fix run_ppapi_ppp_input_event_browser_test and re-enable it.

ppapi/native_client/tests/ppapi_browser/ppp_input_event/ppapi_ppp_input_event.js

Index: ppapi/native_client/tests/ppapi_browser/ppp_input_event/ppapi_ppp_input_event.js
diff --git a/ppapi/native_client/tests/ppapi_browser/ppp_input_event/ppapi_ppp_input_event.js b/ppapi/native_client/tests/ppapi_browser/ppp_input_event/ppapi_ppp_input_event.js
index 3700a509c7cb96fd030d37189f3c25456a98809f..c93414403a65bf2e060df6d32f095e4a9fe1aaba 100644
--- a/ppapi/native_client/tests/ppapi_browser/ppp_input_event/ppapi_ppp_input_event.js
+++ b/ppapi/native_client/tests/ppapi_browser/ppp_input_event/ppapi_ppp_input_event.js
@@ -8,9 +8,8 @@ function setupTests(tester, plugin) {
   //////////////////////////////////////////////////////////////////////////////
 
   // These are the coordinates of the upper-left corner of the nacl plugin
-  // TODO(mball): Avoid hardcoding this location by querying the location
-  // of the plugin.
-  var leftCorner = 8, topCorner = 79
+  var leftCorner = plugin.offsetLeft;
+  var topCorner = plugin.offsetTop;
 
   function simulateMouseEvent(eventName) {
     var event = document.createEvent('MouseEvents');