Add a GUID to base::SharedMemoryHandle.

base/memory/shared_memory_posix.cc

Index: base/memory/shared_memory_posix.cc
diff --git a/base/memory/shared_memory_posix.cc b/base/memory/shared_memory_posix.cc
index 0444e59dba1c9f5ca52df331126ecbf8c47ea6f8..4307a77d94857e5871f9b5c42372e0737d80bc86 100644
--- a/base/memory/shared_memory_posix.cc
+++ b/base/memory/shared_memory_posix.cc
@@ -23,6 +23,7 @@
 #include "base/strings/utf_string_conversions.h"
 #include "base/threading/thread_restrictions.h"
 #include "base/trace_event/trace_event.h"
+#include "base/unguessable_token.h"
 #include "build/build_config.h"
 
 #if defined(OS_ANDROID)
@@ -211,8 +212,10 @@ bool SharedMemory::Create(const SharedMemoryCreateOptions& options) {
   int readonly_mapped_file = -1;
   bool result = PrepareMapFile(std::move(fp), std::move(readonly_fd),
                                &mapped_file, &readonly_mapped_file);
-  shm_ = SharedMemoryHandle::ImportHandle(mapped_file);
-  readonly_shm_ = SharedMemoryHandle::ImportHandle(readonly_mapped_file);
+  shm_ = SharedMemoryHandle(base::FileDescriptor(mapped_file, false),
+                            UnguessableToken::Create());
+  readonly_shm_ = SharedMemoryHandle(
+      base::FileDescriptor(readonly_mapped_file, false), shm_.GetGUID());

[Nico, 2017/05/05 18:34:36]

For posix too I suppose, not just mac.

[erikchen, 2017/05/05 19:29:32]

Done.

   return result;
 }
 
@@ -249,8 +252,13 @@ bool SharedMemory::Open(const std::string& name, bool read_only) {
   int readonly_mapped_file = -1;
   bool result = PrepareMapFile(std::move(fp), std::move(readonly_fd),
                                &mapped_file, &readonly_mapped_file);
-  shm_ = SharedMemoryHandle::ImportHandle(mapped_file);
-  readonly_shm_ = SharedMemoryHandle::ImportHandle(readonly_mapped_file);
+  // This form of sharing shared memory is deprecated. https://crbug.com/345734.
+  // Technically, we should also pass the GUID from the original shared memory
+  // region. Instead, we should just remove all instances of this.

[Nico, 2017/05/05 18:34:36]

Your last comment sounds like you no longer think this is easily possible, maybe
update this comment. (Nice example of "deprecation comments don't work" too.)

[erikchen, 2017/05/05 19:29:32]

Done.

+  shm_ = SharedMemoryHandle(base::FileDescriptor(mapped_file, false),
+                            UnguessableToken::Create());
+  readonly_shm_ = SharedMemoryHandle(
+      base::FileDescriptor(readonly_mapped_file, false), shm_.GetGUID());
   return result;
 }
 #endif  // !defined(OS_ANDROID)