Centralize FrameSinkId allocation in one place

cc/surfaces/frame_sink_id_allocator.h

Index: cc/surfaces/frame_sink_id_allocator.h
diff --git a/cc/surfaces/frame_sink_id_allocator.h b/cc/surfaces/frame_sink_id_allocator.h
new file mode 100644
index 0000000000000000000000000000000000000000..a477829c9bbc00940a735fd38b26a97129df2a8f
--- /dev/null
+++ b/cc/surfaces/frame_sink_id_allocator.h
@@ -0,0 +1,22 @@
+// Copyright 2017 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 CC_SURFACES_FRAME_SINK_ID_ALLOCATOR_H_
+#define CC_SURFACES_FRAME_SINK_ID_ALLOCATOR_H_
+
+#include "cc/surfaces/frame_sink_id.h"
+
+namespace cc {
+
+class FrameSinkIdAllocator {

[Fady Samuel, 2017/02/15 20:20:59]

Class level comment explaining the purpose of this class.

[xlai (Olivia), 2017/02/15 22:38:36]

Done.

+ public:
+  FrameSinkId NextFrameSinkId() { return FrameSinkId(0, next_sink_id_++); }

[boliu, 2017/02/15 19:59:20]

should have a comment here why the first part must be 0

[danakj, 2017/02/15 20:18:10]

It seems very action-at-a-distance to decide 0 here in order to not collide with
RenderWidgetHostImpl (if I am understanding the reasoning correctly?)

It would be more straightforward I think to take the 0 in the constructor, or as
a parameter to this method, and have the callers pass 0 with a comment that 0
will be different than RenderWidgetHostImpl. Also then RWHI could use this
class?

wdyt?

[Fady Samuel, 2017/02/15 20:20:59]

Actually I'd prefer that the client_id be a param into the constructor.

[xlai (Olivia), 2017/02/15 22:38:36]

Done.

+
+ private:
+  uint32_t next_sink_id_ = 1u;

[boliu, 2017/02/15 19:59:20]

DISALLOW_COPY_AND_ASSIGN?

[xlai (Olivia), 2017/02/15 22:38:36]

Done.

+};
+
+}  // namespace cc
+
+#endif  // CC_SURFACES_FRAME_SINK_ID_ALLOCATOR_H_