Fixing several memory leaks in wasm unittests.
Avoiding std::vector::data() as it isn't supported on all
compilers on the bots.
Use EXCEPT_TRUE / EXPECT_FALSE to avoid warnings on some compilers when testing boolean equality.

R=ahaas@chromium.org
BUG=

Review URL: https://codereview.chromium.org/1536603003

Cr-Commit-Position: refs/heads/master@{#32940}