Mojo: Require our public options structs to be aligned like int64_t's.

mojo/public/c/system/buffer.h

 // Copyright 2014 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.
 
 // This file contains types/constants and functions specific to buffers (and in
 // particular shared buffers).
 // TODO(vtl): Reorganize this file (etc.) to separate general buffer functions
 // from (shared) buffer creation.
 //
 // Note: This header should be compilable as C.
@@ skipping 20 matching lines @@
 typedef uint32_t MojoCreateSharedBufferOptionsFlags;
 
 #ifdef __cplusplus
 const MojoCreateSharedBufferOptionsFlags
     MOJO_CREATE_SHARED_BUFFER_OPTIONS_FLAG_NONE = 0;
 #else
 #define MOJO_CREATE_SHARED_BUFFER_OPTIONS_FLAG_NONE \
     ((MojoCreateSharedBufferOptionsFlags) 0)
 #endif
 
-struct MojoCreateSharedBufferOptions {
+MOJO_COMPILE_ASSERT(MOJO_ALIGNOF(int64_t) == 8, int64_t_has_weird_alignment);
+struct MOJO_ALIGNAS(8) MojoCreateSharedBufferOptions {
   uint32_t struct_size;
   MojoCreateSharedBufferOptionsFlags flags;
 };
 MOJO_COMPILE_ASSERT(sizeof(MojoCreateSharedBufferOptions) == 8,
                     MojoCreateSharedBufferOptions_has_wrong_size);
 
 // |MojoDuplicateBufferHandleOptions|: Used to specify parameters in duplicating
 // access to a shared buffer to |MojoDuplicateBufferHandle()|.
 //   |uint32_t struct_size|: Set to the size of the
 //       |MojoDuplicateBufferHandleOptions| struct. (Used to allow for future
@@ skipping 80 matching lines @@
 
 // Unmap a buffer pointer that was mapped by |MojoMapBuffer()|.
 // TODO(vtl): More.
 MOJO_SYSTEM_EXPORT MojoResult MojoUnmapBuffer(void* buffer);  // In.
 
 #ifdef __cplusplus
 }  // extern "C"
 #endif
 
 #endif  // MOJO_PUBLIC_C_SYSTEM_BUFFER_H_