[mojo] Add CreateSharedBuffer method to Broker.

mojo/edk/system/broker_messages.h

Index: mojo/edk/system/broker_messages.h
diff --git a/mojo/edk/system/broker_messages.h b/mojo/edk/system/broker_messages.h
index 0ce0960d685b9fadc8e0cb5c1c0c7adf936bfd2c..1e386cf6c544adbd3e70e8ecf88b4bd6b1d114b2 100644
--- a/mojo/edk/system/broker_messages.h
+++ b/mojo/edk/system/broker_messages.h
@@ -16,35 +16,41 @@ namespace edk {
 // This header defines the message format between ChildBroker and
 // ChildBrokerHost.
 
-#if defined(OS_WIN)
-// Windows only messages needed because sandboxed child processes need the
-// parent's help. They are sent synchronously from child to parent and each have
+// Sandbox processes need the parent's help to create shared buffers.
+// They are sent synchronously from child to parent and each have
 // a response. They are sent over a raw pipe.
-enum WindowsSandboxMessages {
+enum SandboxMessages {

[Anand Mistry (off Chromium), 2016/01/07 04:36:33]

Not your fault, but these should have a uint32_t size declaration. Without it,
an enum size can vary based on platform, and use in a serialised struct could
cause crashes if you transfer between a 32 and 64 bit process. In Chrome,
there's at least one case where this is possible (NaCl, which is always ILP32).

Maybe you can make this change to all the enums here in a separate CL.

Also, I don't see any packed declarations. These should be added to any
serialised structures.

[Eliot Courtney, 2016/01/07 05:01:30]

Acknowledged.

+#if defined(OS_WIN)
   // The reply is two HANDLEs.
   CREATE_PLATFORM_CHANNEL_PAIR = 0,
   // The reply is tokens of the same count of passed in handles.
   HANDLE_TO_TOKEN,
   // The reply is handles of the same count of passed in tokens.
   TOKEN_TO_HANDLE,
+#else
+  // The reply is a PlatformHandle.
+  CREATE_SHARED_BUFFER = 0,
+#endif
 };
 
 // Definitions of the raw bytes sent in messages.
 
 struct BrokerMessage {
   uint32_t size;
-  WindowsSandboxMessages id;
+  SandboxMessages id;
+
+#if defined(OS_WIN)
   // Data, if any, follows.
   union {
     HANDLE handles[1];  // If HANDLE_TO_TOKEN.
     uint64_t tokens[1];  // If TOKEN_TO_HANDLE.
   };
+#else
+  uint32_t num_bytes;  // Size of the shared buffer to create.

[Anand Mistry (off Chromium), 2016/01/07 04:36:33]

Maybe call it shared_buffer_size instead. num_bytes is pretty non-descriptive.

[Eliot Courtney, 2016/01/07 05:01:30]

Done.

+#endif
 };
 
-const int kBrokerMessageHeaderSize =
-  sizeof(uint32_t) + sizeof(WindowsSandboxMessages);
-
-#endif
+const int kBrokerMessageHeaderSize = sizeof(uint32_t) + sizeof(SandboxMessages);
 
 // Route id used for messages between ChildBroker and ChildBrokerHost.
 const uint64_t kBrokerRouteId = 1;