Support running w/ Sky from a local checkout through a config file.

mojo/devtools/common/README.md

 # Devtools
 
 Unopinionated tools for **running**, **debugging** and **testing** Mojo apps.
 
 ## Install
 
 ```
 git clone https://github.com/domokit/devtools.git
 ```
 
@@ skipping 32 matching lines @@
 app, you have to first start the window manager app, then have it embed the app
 you are interested in. It is done as follows using the default window manager:
 
 ```sh
 mojo_run "mojo:window_manager APP_URL"
 ```
 
 By default, `mojo_run` uses `mojo:kiosk_wm` as the default window manager. It
 can be changed using the `--window-manager` flag.
 
-#### Sky apps
-
-To run a [Sky](https://github.com/domokit/sky_engine) app, you need to build
-`sky_viewer.mojo` in a Sky checkout, and indicate the path to the binary using
-the `--map-url` parameter:
-
-```sh
-mojo_run --map-url mojo:sky_viewer=/path/to/sky/viewer "mojo:window_manager APP_URL"
-```
-
-If the app does not declare a shebang indicating that it needs to be run in
-`sky_viewer`, pass `--sky` to map `sky_viewer` as a default content handler for
-dart apps:
-
-```sh
-mojo_run --map-url mojo:sky_viewer=/path/to/sky/viewer "mojo:window_manager APP_URL" --sky
-```
-
-Note that Sky apps will need the --use-osmesa flag to run
-over [chromoting](https://support.google.com/chrome/answer/1649523?hl=en):
-
 ### Debugger
 
 `mojo_debug` allows you to interactively inspect a running shell, collect
 performance traces and attach a gdb debugger.
 
 #### Tracing
 To collect [performance
 traces](https://www.chromium.org/developers/how-tos/trace-event-profiling-tool)
 and retrieve the result:
 
@@ skipping 43 matching lines @@
 ```sh
 mojo_debug device stack
 ```
 
 ## Development
 
 The library is canonically developed [in the mojo
 repository](https://github.com/domokit/mojo/tree/master/mojo/devtools/common),
 https://github.com/domokit/devtools is a mirror allowing to consume it
 separately.