mojo/gpu: use SharedBuffer instead of base::SharedMemory with hacks

mojo/public/cpp/system/core.h

Index: mojo/public/cpp/system/core.h
diff --git a/mojo/public/cpp/system/core.h b/mojo/public/cpp/system/core.h
index 70221107ab0a2d6ee332d461294840c34c601d55..a5bfb399a7c0c412615f8b439fcf4cf2a4852ff9 100644
--- a/mojo/public/cpp/system/core.h
+++ b/mojo/public/cpp/system/core.h
@@ -404,14 +404,14 @@ inline MojoResult CreateSharedBuffer(
 // manually. (The template enforces that the in and out handles to be of the
 // same type.)
 template <class BufferHandleType>
-inline MojoResult DuplicatedBuffer(
+inline MojoResult DuplicateBuffer(
     BufferHandleType buffer,
     const MojoDuplicateBufferHandleOptions* options,
     ScopedHandleBase<BufferHandleType>* new_buffer) {
   assert(new_buffer);
   BufferHandleType handle;
-  MojoResult rv = MojoDuplicateSharedBuffer(buffer.value(), options,
-                                            handle.mutable_value());
+  MojoResult rv = MojoDuplicateBufferHandle(
+      buffer.value(), options, handle.mutable_value());
   // Reset even on failure (reduces the chances that a "stale"/incorrect handle
   // will be used).
   new_buffer->reset(handle);
@@ -424,7 +424,7 @@ inline MojoResult MapBuffer(BufferHandleType buffer,
                             uint64_t num_bytes,
                             void** pointer,
                             MojoMapBufferFlags flags) {
-  assert(buffer);
+  assert(buffer.is_valid());
   return MojoMapBuffer(buffer.value(), offset, num_bytes, pointer, flags);
 }