Add Git SHA to Android BuildConfig.

gistfile1.txt

def gitSha = {
    'git rev-parse --short HEAD'.execute().text.trim()
}()

def buildTime() {
    def df = new Date().format("yyyyMMddHHmm", TimeZone.getTimeZone("UTC"))
    return df
}

android {
    ...
    defaultConfig {
        ...
        buildConfigField 'String','BUILD_TIME', "\"${buildTime()}\""
        buildConfigField 'String','GIT_SHA', "\"${gitSha}\""
        ...
    }

Adapted from https://plus.google.com/+JakeWharton/posts/6f5TcVPRZij