Correct dump_dependency_json on windows.
Correct dump_dependency_json on windows.

Fills in variables that are supplied by other generators and relied upon
by existing gyp files.

Patch by twiz@chromium.org.
old8xp/gyp_from_google,old8xp/gyp_from_google,old8xp/gyp_from_google,old8xp/gyp_from_google,old8xp/gyp_from_google