Added PointerEvent firing on touch events.

Source/core/events/PointerEventUtils.h

+// Copyright 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 PointerEventUtils_h
+#define PointerEventUtils_h
+
+#include "wtf/ListHashSet.h"
+
+namespace blink {
+
+/**
+  Helper class for tracking the primary pointer id for each type of PointerEvents.
+*/
+class PointerIdManager {
+public:
+    // TODO(mustaq): This should live in PointerEvent.h but can't use it there
+    // w/o changing the corresponding type in PointerEvent.idl. Investigate.

[Rick Byers, 2015/06/16 17:25:39]

Note there is a difference.  At the PointerEvent API level, the "type" is a
string because JS can add arbitrary values.  But here we're not interested in
tracking the primary pointer ID for arbitrary pointer types, only for the
specific pointer types blink supports natively.  So it makes some sense that
there are two different definitions.

[mustaq, 2015/06/16 20:18:43]

What about adding a new method pointerTypeEnum() in PointerEvent.h, in addition
to existing pointerType()? We would be able to avoid, at least in our codebase,
the use of strings for what is otherwise an enum.

It's not clear to me why the PE spec uses free-form strings, could be an "enum
of strings" instead, as in:
https://code.google.com/p/chromium/codesearch#chromium/src/third_party/WebKit...

[Rick Byers, 2015/06/18 17:40:07]

It's because we want script to be able to fire different types of pointer
events, effectively making pointer events extensible.  Eg. ideally leap motion
could create a library that generates PointerEvent objects with
pointertype="depthcamera" (maybe built on top of some low-level USB API or
something).

That said, I think there would be value in changing the spec to combine a fixed
enum with a custom string as a union type.  Then the pre-defined values are
still concreted specified by the IDL (and could perhaps be optimized in a
type-safe language) while still permitting extensibility.
Sure, that's fine with me.  You could even keep an enum value internally and
only fill in the string in the unusual case that script sets it to a
non-standard value.  Anyway feel free to leave this TODO here and make such a
change in a future CL.

[mustaq, 2015/06/18 18:20:53]

Acknowledged.

+    enum PointerType {
+        PointerTypeUnknown = 0,
+        PointerTypeMouse,
+        PointerTypePen,
+        PointerTypeTouch,
+        PointerTypeLastEntry // Must be the last entry in the list
+    };
+
+    PointerIdManager();
+    ~PointerIdManager();
+    void clear();
+    void add(PointerType, unsigned);
+    void remove(PointerType, unsigned);
+    bool isPrimary(PointerType, unsigned);
+
+private:
+    ListHashSet<unsigned> m_ids[PointerTypeLastEntry];
+    bool m_hasPrimaryId[PointerTypeLastEntry];
+};
+
+} // namespace blink
+
+#endif // PointerEventUtils_h