Add WebPointerProperties type.

public/web/WebPointerProperties.h

+// Copyright (c) 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef WebPointerProperties_h
+#define WebPointerProperties_h
+
+namespace blink {
+
+// TODO(e_hakkinen): Replace WebTouchEvent with WebPointerEvent, remove
+//                   WebTouchEvent and WebTouchPoint and merge this into

[Rick Byers, 2015/07/09 00:44:26]

nit: don't add extra space at the beginning of these two lines.

[USE eero AT chromium.org, 2015/07/14 23:44:13]

Done.

+//                   WebPointerEvent.
+class WebPointerProperties {

[Rick Byers, 2015/07/09 00:44:27]

Please add a high level description that describes the motivation here.  Eg.
"This class encapsulates the properties that are common between mouse events and
touch points as we transition towards the unified pointer event model.".

[USE eero AT chromium.org, 2015/07/14 23:44:13]

Done.

+public:
+    WebPointerProperties()
+        : button(ButtonNone)
+        , id(0)
+        , radiusX(0.f)
+        , radiusY(0.f)
+        , force(0.f)
+    {
+    }
+
+    enum Button {
+        ButtonNone = -1,
+        ButtonLeft,
+        ButtonMiddle,
+        ButtonRight
+    };
+
+    Button button;
+
+    int id;
+    float radiusX;

[mustaq, 2015/07/09 17:47:01]

A quick suggestion around the touch orientation properties (radiusX + radiusY +
rotationAngle): I think it makes the most sense to keep all three of these
together because the angle is meaningless when we are unaware of non-uniform
radii. 

We have two ways to fix this:
(a) leave radiusX and radiusY in WebTouchPoint, or
(b) move even rotationAngle from WebTouchPoint to here.

I am slightly biased towards Option(b) because I believe we will ultimately
reach there. But Option(a) also makes sense for our immediate goal (stylus
support).

Thoughts?

+    float radiusY;
+    float force;
+};
+
+} // namespace blink
+
+#endif