Implement MojoGetBufferInformation(), part 3.

This hooks up Core::GetBufferInformation() to all the thunks, etc.

R=smklein@chromium.org, vardhan@google.com
BUG=#501

Review URL: https://codereview.chromium.org/1778753002 .
diff --git a/mojo/edk/embedder/system_impl_private_entrypoints.cc b/mojo/edk/embedder/system_impl_private_entrypoints.cc
index e772165..3a159ab 100644
--- a/mojo/edk/embedder/system_impl_private_entrypoints.cc
+++ b/mojo/edk/embedder/system_impl_private_entrypoints.cc
@@ -242,6 +242,16 @@
                                      MakeUserPointer(new_buffer_handle));
 }
 
+MojoResult MojoSystemImplGetBufferInformation(MojoSystemImpl system,
+                                              MojoHandle buffer_handle,
+                                              MojoBufferInformation* info,
+                                              uint32_t info_num_bytes) {
+  mojo::system::Core* core = static_cast<mojo::system::Core*>(system);
+  DCHECK(core);
+  return core->GetBufferInformation(buffer_handle, MakeUserPointer(info),
+                                    info_num_bytes);
+}
+
 MojoResult MojoSystemImplMapBuffer(MojoSystemImpl system,
                                    MojoHandle buffer_handle,
                                    uint64_t offset,