Sometimes, Google just baffles me. The lack of direction in their product lines makes me shake my head.
We have several distinct software platforms:
1) Android. Development in XML with Java used as glue to hold everything together. Unless you don't. You can use standard C libraries and call the Linux kernel directly, bypassing the Dalvik Java VM.
4) But Let's not forget the 4th platform in the trio: Google's Go language is clearly a contender, and it's designed to replace C, except for a few bone-headed decisions like linking everything statically resulting in enormous binaries. Because you really, really need to have the same library installed once for every app installed, because that way you get to recompile everything installed on your system any time a security update comes out for your favorite library. Except that, of course there are exceptions here, too.
And most importantly, you cannot target all these platforms with any single codebase written in any language. It's like they are trying to make their product suite as difficult as just using products from multiple vendors anyway.
It's really quite simple. A lot of Google projects started from a handful of people going "you know what would be a cool idea?" and doing it with very little approval or red tape (the fabled 20% time). That's certainly the only explanation I can think of for DART, at any rate.
Go is basically what you get when you hire a former Plan 9 developer, expose him to Google's internal hermetic build system (where a 100MiB binary is small), then let him build cool stuff to keep him from getting bored.
Disclaimer: I work at Google but do not speak for my employer. I don't work on any of the teams mentioned in your post. The information in this post is already available to the public in various places.