Merge to XFA: Pass v8::Isolate to PDFium at init time.

New code changes in JS_Runtime.cpp.

(cherry picked from commit 3dedace9623fef6161a8666e53a4ab2b9be61e4c)
Original Review URL: https://codereview.chromium.org/1367033002 .

Also merge to XFA: Run FXJS_V8 embedder tests against a shared isolate,
since the two go together.

(cherry picked from commit 4ea721cb7954898a9722c389dae86c62957352d0)
Original Review URL: https://codereview.chromium.org/1377293004 .

R=thestig@chromium.org

Review URL: https://codereview.chromium.org/1381633008 .
11 files changed