Create pdfium_unittests binary.

Create pdfium_unittests binary.

PDFium has not yet had a unit-tests binary, so introduce one based on
the typical gtest framework. Also provide a small initial test fragment
for fxcrt strings for instructional purposes.

Naturally, doing so kicked out one corner case that isn't handled, we'll
fix that in a separate patch.

This is a small part of the testing strategy tracking bug.
BUG=https://code.google.com/p/pdfium/issues/detail?id=62
R=brucedawson@chromium.org, palmer@chromium.org

Committed: https://pdfium.googlesource.com/pdfium/+/336991da7a3d5682a572c01e0a149b6990d05594

[Tom Sepez, 2014-12-29 20:11:52]

tsepez@chromium.org changed reviewers:
+ brucedawson@chromium.org, jam@chromium.org

[Tom Sepez, 2014-12-29 20:11:52]

Please review.

[palmer, 2014-12-29 20:22:57]

palmer@chromium.org changed reviewers:
+ palmer@chromium.org

[palmer, 2014-12-29 20:22:57]

LGTM. Thanks!!

[brucedawson, 2014-12-29 20:45:29]

lgtm

[Tom Sepez, 2014-12-29 21:56:19]

Committed patchset #1 (id:1) manually as
336991da7a3d5682a572c01e0a149b6990d05594 (presubmit successful).