I'm not sure what distinction you're making between Dart and languages that "compile in the browser". You linked to Jeremy Ashkenas' list of languages which compile to Javascript, yet that list includes Java, Python, and even Dart
Edit: Are you referring to languages that you can compile to Javascript by including a script in the HTML? I remember doing this with React, before I set up a build tool to my project. If that's what you're referring to, I'm not sure it's such a huge factor. For one thing, I am not aware of any technical reasons why Dart can't do this as well. For another thing, I don't think compiling in the browser is all that popular. Most front-end developers have embraced build tools like Gulp, Grunt, and Webpack which allow compile to Javascript. Compiling in the browser is also not as performant.
Edit: Are you referring to languages that you can compile to Javascript by including a script in the HTML? I remember doing this with React, before I set up a build tool to my project. If that's what you're referring to, I'm not sure it's such a huge factor. For one thing, I am not aware of any technical reasons why Dart can't do this as well. For another thing, I don't think compiling in the browser is all that popular. Most front-end developers have embraced build tools like Gulp, Grunt, and Webpack which allow compile to Javascript. Compiling in the browser is also not as performant.