Add GenericSharedMemoryId and use w/ GpuMemoryBuffer

ui/gfx/generic_shared_memory_id.h

Index: ui/gfx/generic_shared_memory_id.h
diff --git a/ui/gfx/generic_shared_memory_id.h b/ui/gfx/generic_shared_memory_id.h
new file mode 100644
index 0000000000000000000000000000000000000000..9aa226f40cee94e032149606ae8cb1465aeb26fa
--- /dev/null
+++ b/ui/gfx/generic_shared_memory_id.h
@@ -0,0 +1,54 @@
+// 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 UI_GFX_GENERIC_SHARED_MEMORY_ID_H_
+#define UI_GFX_GENERIC_SHARED_MEMORY_ID_H_
+
+#include "base/trace_event/memory_allocator_dump.h"
+#include "ui/gfx/gfx_export.h"
+
+namespace gfx {
+
+// Defines an ID type which is used across all types of shared memory
+// allocations in content/. This ID type is in ui/gfx, as components outside
+// content/ may need to hold an ID (but should not generate one).
+class GFX_EXPORT GenericSharedMemoryId {
+ public:
+  int id;
+
+  // Invalid ID is -1 to match semantics of base::StaticAtomicSequenceNumber.
+  GenericSharedMemoryId() : id(-1) {}
+  explicit GenericSharedMemoryId(int id) : id(id) {}
+  GenericSharedMemoryId(const GenericSharedMemoryId& other) = default;
+  GenericSharedMemoryId& operator=(const GenericSharedMemoryId& other) =
+      default;
+
+  bool operator==(const GenericSharedMemoryId& other) const {
+    return id == other.id;
+  }
+
+  bool operator<(const GenericSharedMemoryId& other) const {
+    return id < other.id;
+  }
+};
+
+// Generates GUID which can be used to trace shared memory using its
+// GenericSharedMemoryId.
+GFX_EXPORT base::trace_event::MemoryAllocatorDumpGuid
+GetGenericSharedMemoryGUIDForTracing(
+    uint64_t tracing_process_id,
+    GenericSharedMemoryId generic_shared_memory_id);
+
+}  // namespace gfx
+
+namespace BASE_HASH_NAMESPACE {
+template <>
+struct hash<gfx::GenericSharedMemoryId> {
+  size_t operator()(gfx::GenericSharedMemoryId key) const {
+    return BASE_HASH_NAMESPACE::hash<int>()(key.id);
+  }
+};
+}  // namespace BASE_HASH_NAMESPACE
+
+#endif  // UI_GFX_GENERIC_SHARED_MEMORY_ID_H_