Adds sync brokering to Windows EDK

mojo/edk/embedder/platform_shared_buffer.cc

Index: mojo/edk/embedder/platform_shared_buffer.cc
diff --git a/mojo/edk/embedder/platform_shared_buffer.cc b/mojo/edk/embedder/platform_shared_buffer.cc
index 53d8edc0f6238d3b4f13cfbd6d67183276ad3025..58af44df8f8c2763ce50a135c01b744e62fdd844 100644
--- a/mojo/edk/embedder/platform_shared_buffer.cc
+++ b/mojo/edk/embedder/platform_shared_buffer.cc
@@ -253,21 +253,28 @@ bool PlatformSharedBuffer::InitFromPlatformHandle(
 bool PlatformSharedBuffer::InitFromPlatformHandlePair(
     ScopedPlatformHandle rw_platform_handle,
     ScopedPlatformHandle ro_platform_handle) {
-#if defined(OS_WIN) || defined(OS_MACOSX)
+#if defined(OS_MACOSX)
   NOTREACHED();
   return false;
-#else
-  DCHECK(!shared_memory_);
+#else  // defined(OS_MACOSX)
 
+#if defined(OS_WIN)
+  base::SharedMemoryHandle handle(rw_platform_handle.release().handle,
+                                  base::GetCurrentProcId());
+  base::SharedMemoryHandle ro_handle(ro_platform_handle.release().handle,
+                                     base::GetCurrentProcId());
+#else  // defined(OS_WIN)
   base::SharedMemoryHandle handle(rw_platform_handle.release().handle, false);
-  shared_memory_.reset(new base::SharedMemory(handle, false));
-
   base::SharedMemoryHandle ro_handle(ro_platform_handle.release().handle,
                                      false);

[Will Harris, 2016/09/13 23:54:43]

I think this is correct...? as presumably you create the handle rw here then dup
it to a ro one on L274 but can you add a comment as it looks wonky to create a
ro_handle with |read_only| set to false.

Unless this is wrong, in which case why have the two stage create?

[Ken Rockot(use gerrit already), 2016/09/14 19:57:04]

The SharedMemoryHandle constructor doesn't know anything about read_only. The
|false| in these constructors is for |auto_close| (see base::FileDescriptor).
It's correct since we pass ownership of the handles into base::SharedMemory and
don't want them scoped to the local handle here.

[Will Harris, 2016/09/14 20:24:21]

Acknowledged.

-  ro_shared_memory_.reset(new base::SharedMemory(ro_handle, true));
+#endif  // defined(OS_WIN)
 
+  DCHECK(!shared_memory_);
+  shared_memory_.reset(new base::SharedMemory(handle, false));
+  ro_shared_memory_.reset(new base::SharedMemory(ro_handle, true));
   return true;
-#endif
+
+#endif  // defined(OS_MACOSX)
 }
 
 void PlatformSharedBuffer::InitFromSharedMemoryHandle(