Mojo: Add a C++-style SharedBuffer API.

mojo/public/cpp/system/buffer.h

Index: mojo/public/cpp/system/buffer.h
diff --git a/mojo/public/cpp/system/buffer.h b/mojo/public/cpp/system/buffer.h
index a2d524e20d13e28c1d526c5da6eb430f3d83955a..27ba814a6172786f8d3eda184c68a56667c9299d 100644
--- a/mojo/public/cpp/system/buffer.h
+++ b/mojo/public/cpp/system/buffer.h
@@ -14,27 +14,61 @@
 
 #include <stdint.h>
 
+#include <memory>
+
 #include "base/compiler_specific.h"
 #include "base/logging.h"
 #include "mojo/public/c/system/buffer.h"
 #include "mojo/public/cpp/system/handle.h"
 
 namespace mojo {
+namespace internal {
+
+struct Unmapper {
+  void operator()(void* buffer) {
+    MojoResult result = MojoUnmapBuffer(buffer);
+    DCHECK_EQ(MOJO_RESULT_OK, result);
+  }
+};
+
+}  // namespace internal
+
+using ScopedSharedBufferMapping = std::unique_ptr<void, internal::Unmapper>;
+
+class SharedBufferHandle;
+
+typedef ScopedHandleBase<SharedBufferHandle> ScopedSharedBufferHandle;
 
 // A strongly-typed representation of a |MojoHandle| referring to a shared
 // buffer.
 class SharedBufferHandle : public Handle {
  public:
+  enum class AccessMode {
+    READ_WRITE,
+    READ_ONLY,
+  };
+
   SharedBufferHandle() {}
   explicit SharedBufferHandle(MojoHandle value) : Handle(value) {}
 
   // Copying and assignment allowed.
+
+  // Clones this shared buffer handle. If |access_mode| is READ_ONLY or this is
+  // a read-only handle, the new handle will be read-only. On failure, this will
+  // return an empty result.
+  ScopedSharedBufferHandle Clone(AccessMode = AccessMode::READ_WRITE) const;
+
+  // Maps |size| bytes of this shared buffer. On failure, this will return a
+  // null mapping.
+  ScopedSharedBufferMapping Map(uint64_t size) const;
+
+  // Maps |size| bytes of this shared buffer, starting |offset| bytes into the
+  // buffer. On failure, this will return a null mapping.
+  ScopedSharedBufferMapping MapAtOffset(uint64_t size, uint64_t offset) const;
 };
 
 static_assert(sizeof(SharedBufferHandle) == sizeof(Handle),
               "Bad size for C++ SharedBufferHandle");
-
-typedef ScopedHandleBase<SharedBufferHandle> ScopedSharedBufferHandle;
 static_assert(sizeof(ScopedSharedBufferHandle) == sizeof(SharedBufferHandle),
               "Bad size for C++ ScopedSharedBufferHandle");