Likely was "true" in the original source (and the source in separate files) and was replaced by some minifier. Not clear if these are the files verbatim or if it was automatically formatted from minified js.
It is one of the peephole optimizations that Closure Compiler performs to save some space (read: 2-3 characters) in the final output: http://code.google.com/p/closure-compiler/source/browse/src/.... The compiler actually has a lot of cool little tricks like that to save space (since saving even a few bytes for a property like, say, Gmail, can translate to very large numbers very quickly)