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

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

Committed: https://pdfium.googlesource.com/pdfium/+/a72e8e2c4392df725c7e35ed1ae3f891e79e49ec

[Tom Sepez, 2015-10-06 16:26:48]

Lei, small amount of new code here.

[Lei Zhang, 2015-10-06 23:18:55]

lgtm

https://codereview.chromium.org/1381633008/diff/20001/fpdfsdk/src/jsapi/fxjs_...
File fpdfsdk/src/jsapi/fxjs_v8_embeddertest.cpp (right):

https://codereview.chromium.org/1381633008/diff/20001/fpdfsdk/src/jsapi/fxjs_...
fpdfsdk/src/jsapi/fxjs_v8_embeddertest.cpp:33: v8::Locker locker(m_pIsolate);
BTW, we have |locker| here but not on the main branch.

https://codereview.chromium.org/1381633008/diff/20001/fpdfsdk/src/jsapi/fxjs_...
fpdfsdk/src/jsapi/fxjs_v8_embeddertest.cpp:59: v8::Locker locker(isolate());
Ditto.

[Tom Sepez, 2015-10-06 23:22:50]

> BTW, we have |locker| here but not on the main branch.
> 
I've always assumed that this is unique to XFA; JS can be entered by both
fpdfsdk and xfa hence the lock to keep one out while the other is running.  But
I'm not 100% on this.

[Tom Sepez, 2015-10-07 17:17:58]

Committed patchset #2 (id:20001) manually as
a72e8e2c4392df725c7e35ed1ae3f891e79e49ec (presubmit successful).