Implement WASM support on big-endian platforms. WASM has
an implicit requirement that it is running on little-endian
machine. We achieve WASM support on BE by keeping data
in memory in little-endian order, and changing data
endianness before storing to memory and after loading from
memory.

BUG=

Review-Url: https://codereview.chromium.org/2034093002
Cr-Commit-Position: refs/heads/master@{#37065}