Splitting the file into two strings in shader_translator complicated
testing line/file numbering related functionality with it, since each
chunk passed to ShCompile has its own file number and line numbering.
These are exposed to the preprocessor in __FILE__ and __LINE__ predefined
macros.

Just supply the file to ShCompile in a single string. Also, since the
original motivation for splitting the string seems to have been to
exercise ShCompile with multiple strings, add a new unit test that
ensures that ShCompile handles multiple strings as expected.

BUG=angleproject:989
TEST=angle_unittests

Change-Id: I31d24925ec85ca3411e537df25a985f09737403e
Reviewed-on: https://chromium-review.googlesource.com/297251Tested-by: Olli Etuaho <oetuaho@nvidia.com>
Reviewed-by: Zhenyao Mo <zmo@chromium.org>