Include external touchscreen vid/pid in UMA hardware profile

ui/events/x/touch_factory_x11.h

Index: ui/events/x/touch_factory_x11.h
diff --git a/ui/events/x/touch_factory_x11.h b/ui/events/x/touch_factory_x11.h
index ed62c6d247f59ec6cefcd76b775c1e8623ad686d..4d8a989fd8f87fe20a68a3c89e6a990ad5c6abaf 100644
--- a/ui/events/x/touch_factory_x11.h
+++ b/ui/events/x/touch_factory_x11.h
@@ -7,6 +7,8 @@
 
 #include <bitset>
 #include <map>
+#include <set>
+#include <utility>
 #include <vector>
 
 #include "base/timer/timer.h"
@@ -72,6 +74,11 @@ class EVENTS_BASE_EXPORT TouchFactory {
   // Whether any touch device is currently present and enabled.
   bool IsTouchDevicePresent();
 
+  // Pairs of <vendor id, product id> of external touch screens.
+  const std::set<std::pair<int, int> >& GetTouchscreenIds() const {
+    return touchscreen_ids_;
+  }
+
   // Return maximum simultaneous touch points supported by device.
   int GetMaxTouchPoints() const;
 
@@ -89,6 +96,8 @@ class EVENTS_BASE_EXPORT TouchFactory {
   // Requirement for Singleton
   friend struct DefaultSingletonTraits<TouchFactory>;
 
+  void CacheTouchscreenIds(Display* display, int id);
+
   // NOTE: To keep track of touch devices, we currently maintain a lookup table
   // to quickly decide if a device is a touch device or not. We also maintain a
   // list of the touch devices. Ideally, there will be only one touch device,
@@ -118,6 +127,9 @@ class EVENTS_BASE_EXPORT TouchFactory {
   // capable.
   std::map<int, bool> touch_device_list_;
 
+  // Touch screen <vid, pid>s.
+  std::set<std::pair<int, int> > touchscreen_ids_;
+
   // Maximum simultaneous touch points supported by device. In the case of
   // devices with multiple digitizers (e.g. multiple touchscreens), the value
   // is the maximum of the set of maximum supported contacts by each individual