Hi,
We cannot know for sure what will happen regarding Dart in Chrome by default. What we could speculate is that Dart could continue to be used in a sandbox mode like if it was in a browser environment, except that it would power things in hardware/software developed by Google. Now whether Dart could land in a form of plugin on Chrome, perhaps. After all, Chrome hosts apps and so on. But at least at the beginning, I doubt Dart would be enabled by default on the public web. All browsers have been "at war" against plugins. Somehow my Chrome wants to ask permission to run Flash on sites now, for example. So it would be kind of hypocrisy to deny other companies from running their plugins while one tries to push their own plugin forward.
So most of Dart will have to be compiled to JavaScript to really compete for market share with other alternatives. Unless the Dart VM is hosted in a sandbox on Android or Chrome app environment. ;-)
I like for example the recent experiment they started called Fletch. They said they were also trying for a fast interpreter. I liked both of those as things to look forward to in 2015.
Ultimately the web is kind of a democracy, right? Minorities may not get their way. For example, I am bummed that they didn't manage to add mixins to ECMAScript 6, and now folks will have to come up with their own methods around that.
The goal of running games at max speed in the web is not one that interests many companies, I'm afraid. There is also the hope that one could target asm.js for that. So maybe if Dart had a backend for asm.js it could work.
Cheers,
Joao