[mojo] Add CreateSharedBuffer method to Broker.

mojo/edk/system/broker_messages.h

 // 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 MOJO_EDK_SYSTEM_BROKER_MESSAGES_H_
 #define MOJO_EDK_SYSTEM_BROKER_MESSAGES_H_
 
 #include <stdint.h>
 
 #include "base/compiler_specific.h"
 #include "base/process/process_handle.h"
 
 namespace mojo {
 namespace edk {
 
 // Pack all structs here.
 #pragma pack(push, 1)
 
 // This header defines the message format between ChildBroker and
 // ChildBrokerHost.
 
+// 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 SandboxMessages : uint32_t {
 #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
-// a response. They are sent over a raw pipe.
-enum WindowsSandboxMessages : uint32_t {
   // 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 shared_buffer_size;  // Size of the shared buffer to create.
+#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;
 
 // Multiplexing related messages. They are all asynchronous messages.
 // They are sent over RawChannel.
 enum MultiplexMessages : uint32_t {
   // Messages from child to parent.
 
   // Tells the parent that the given pipe id has been bound to a
@@ skipping 44 matching lines @@
   MultiplexMessages type;  // PEER_DIED
   uint64_t pipe_id;
 };
 
 #pragma pack(pop)
 
 }  // namespace edk
 }  // namespace mojo
 
 #endif  // MOJO_EDK_SYSTEM_BROKER_MESSAGES_H_