Besides adding accessors get_origin() and set_origin(), it creates easier test
accessors is_wasm() and is_asm_js().

This allows the possibility of caching boolean flags for is_wasm() and
is_asm_js() without having to change any code except for the files containing
the class definition for WasmModule.

BUG= v8:6152
R=bbudge@chromium.org,mtrofin@chromium.org

Review-Url: https://codereview.chromium.org/2771803005
Cr-Commit-Position: refs/heads/master@{#44130}