src/copy_compiler_dll.bat defines the case of the file
copied to the build output directory. It is then referenced
by build systems. The case must be consistent with the uses,
in isolate files, and the .gypi file defining output.

BUG=390210

Change-Id: I90c305a0c3663d46d2448e0adfa3103d0ce457d1
Reviewed-on: https://chromium-review.googlesource.com/206305Reviewed-by: Shannon Woods <shannonwoods@chromium.org>
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Tested-by: Geoff Lang <geofflang@chromium.org>