Add support for a GYP_DEFINES environment variable as a way to pass in default values for definitions. Review URL: http://codereview.chromium.org/62128
Add support for a GYP_DEFINES environment variable as a way to pass in
default values for definitions.
Review URL: http://codereview.chromium.org/62128

csulmone/gyp,csulmone/gyp,csulmone/gyp,csulmone/gyp