Add GenericSharedMemoryId and use w/ GpuMemoryBuffer

ui/gfx/gpu_memory_buffer.h

Index: ui/gfx/gpu_memory_buffer.h
diff --git a/ui/gfx/gpu_memory_buffer.h b/ui/gfx/gpu_memory_buffer.h
index 263a0ef41da40ddd140556c2ccc0d73d51a30afe..6d2738d7ebb9bc4c30bea0e28721aba38c737fb6 100644
--- a/ui/gfx/gpu_memory_buffer.h
+++ b/ui/gfx/gpu_memory_buffer.h
@@ -9,6 +9,7 @@
 #include "base/trace_event/memory_dump_manager.h"
 #include "build/build_config.h"
 #include "ui/gfx/buffer_types.h"
+#include "ui/gfx/generic_shared_memory_tracing_id.h"
 #include "ui/gfx/gfx_export.h"
 
 extern "C" typedef struct _ClientBuffer* ClientBuffer;
@@ -24,7 +25,7 @@ enum GpuMemoryBufferType {
   GPU_MEMORY_BUFFER_TYPE_LAST = OZONE_NATIVE_PIXMAP
 };
 
-using GpuMemoryBufferId = int32;
+using GpuMemoryBufferId = gfx::GenericSharedMemoryTracingId;

[reveman, 2015/08/13 08:24:44]

I'm not a fan of using something called a "tracing" Id for something non-tracing
related. GpuMemoryBufferId is used to identify GMBs. We need it independent of
tracing.

[danakj, 2015/08/13 17:29:50]

It is a tracing id though. For GpuMemoryBuffers we happen to use that tracing id
as a main id. In other places we don't. I thought this captures it really well?

[reveman, 2015/08/13 20:12:23]

I don't know what it means to be a tracing id. This is the main id in all cases
I'm currently aware that we intend to use it. We're just interested in making
the use of ids for various types of shared memory consistent and allocated in a
way that allows them to optionally be used for tracing. I think we should be
able to use it for some shared memory without having to add tracing support for
the memory.

By naming this a "tracing" id, we're making all the systems -including the
GpuMemoryBuffer framework- that use it as its main id depend on tracing
implicitly. I think that's incorrect and confusing.

[danakj, 2015/08/13 20:30:37]

My understanding is that there are shared memory types that will have this id
attached to them for no reason other than for tracing. And that GpuMemoryBuffer
just happens to use this for other things too, as it's main id.

[reveman, 2015/08/13 20:52:23]

GMBs, DiscardableMemory, IOSurfaces, SurfaceTextures, etc. will use this as a
real id that is required for these systems to work. Maybe we'll use it for
something that is currently not tracked by ids just to add tracing support in
the future but we can always "using XResourceTracingId =
gfx::GenericSharedMemoryId" if we want to make it explicit that it's only used
for tracing in those cases.

[danakj, 2015/08/13 21:20:26]

OK if that's the case then I guess you're right and naming it for Tracing
doesn't make sense.

 
 struct GFX_EXPORT GpuMemoryBufferHandle {
   GpuMemoryBufferHandle();