Add a GUID to base::SharedMemoryHandle.

base/memory/shared_memory.h

Index: base/memory/shared_memory.h
diff --git a/base/memory/shared_memory.h b/base/memory/shared_memory.h
index 89bc24ac0230e7facf3f021595a6613fa2a22001..35067e6aaeab848080c681fa729f7853df720f3c 100644
--- a/base/memory/shared_memory.h
+++ b/base/memory/shared_memory.h
@@ -63,8 +63,10 @@ struct BASE_EXPORT SharedMemoryCreateOptions {
   bool share_read_only = false;
 };
 
-// Platform abstraction for shared memory.  Provides a C++ wrapper
-// around the OS primitive for a memory mapped file.
+// Platform abstraction for shared memory.
+// SharedMemory consumes a SharedMemoryHandle [potentially one that it created]
+// to map a shared memory OS resource into the virtual address space of the
+// current process.
 class BASE_EXPORT SharedMemory {
  public:
   SharedMemory();