Fix .d file outputs, add support for asserting outputs.

Fixes .d file generation by putting the first output file name as the
destination file, rather than the .d file itself.

Adds support for asserting that given files are in the output. This allows
the user of the build tool to assume that certain output files will be
generated while providing a way to catch errors.

R=thakis@chromium.org
Review=https://codereview.chromium.org/407693002/


git-svn-id: http://grit-i18n.googlecode.com/svn/trunk@171 7262f16d-afe8-6277-6482-052fa10e57b1