Chromium side of maxTouchPoints implementation.

ui/base/touch/touch_device.h

Index: ui/base/touch/touch_device.h
diff --git a/ui/base/touch/touch_device.h b/ui/base/touch/touch_device.h
index 8cc4b7d615ddc09ebef3f30ba2d8f5816aba42c9..b06c56462e61f08d81e1d3d1a9c01d9321a97658 100644
--- a/ui/base/touch/touch_device.h
+++ b/ui/base/touch/touch_device.h
@@ -9,9 +9,23 @@
 
 namespace ui {
 
+// TODO(sblom): This is non-standard, and should be removed before
+// RuntimeEnabledFlags::PointerEventsMaxTouchPoints is marked stable.
+// Tracked by: http://crbug.com/308649
+const int kMaxTouchPointsUnknown = -1;
+
 // Returns true if a touch device is available.
 UI_EXPORT bool IsTouchDevicePresent();
 
+// Returns the maximum number of simultaneous touch contacts supported
+// by the device. In the case of devices with multiple digitizers (e.g.
+// multiple touchscreens), the value MUST be the maximum of the set of
+// maximum supported contacts by each individual digitizer.
+// For example, suppose a device has 3 touchscreens, which support 2, 5,
+// and 10 simultaneous touch contacts, respectively. This returns 10.
+// http://www.w3.org/TR/pointerevents/#widl-Navigator-maxTouchPoints
+UI_EXPORT int MaxTouchPoints();
+
 }  // namespace ui
 
 #endif  // UI_BASE_TOUCH_TOUCH_DEVICE_H_