In the article they they are doing both. People from chrome team said they are doing asm.js.
"Q: How does SoundScript compare to asm.js?
A: They have different goals: asm.js is a low-level language designed to be a compilation target for other (mostly low-level) languages. SoundScript is a user-facing type system for direct use of JavaScript as a high-level language. Both are complementary, both are useful, and V8 is committed to both."
"Q: How does SoundScript compare to asm.js? A: They have different goals: asm.js is a low-level language designed to be a compilation target for other (mostly low-level) languages. SoundScript is a user-facing type system for direct use of JavaScript as a high-level language. Both are complementary, both are useful, and V8 is committed to both."