Add mojo_run --embed APP_URL and update wm urls.

README.md

 Mojo
 ====
 
 Mojo is an effort to extract a common platform out of Chrome's renderer and
 plugin processes that can support multiple types of sandboxed content, such as
 HTML, Pepper, or NaCl.
 
 ## Set-up and code check-out
 
 The instructions below only need to be done once. Note that a simple "git clone"
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 Some applications can be run directly from the source tree. The development
 server serves the `src` directory, allowing to refer to these apps. For
 instance, this command serves a dart Mojo app from the source at
 `examples/dart/device_info/main.dart`:
 
 ```sh
 mojo_run https://core.mojoapps.io/examples/dart/device_info/main.dart [--android]
 ```
 
 Some applications are meant to be run embedded in a **window manager**. To run
-these, pass their urls as arguments for `mojo:window_manager`, which is a
-special url that `mojo_run` maps to a real window manager (
-https://core.mojoapps.io/kiosk_wm.mojo) for you:
+these, you can pass the app url using the `--embed` flag. This will run the
+window manager and pass the given url to it:
 
 ```sh
-devtools/common/mojo_run "mojo:window_manager https://core.mojoapps.io/ganesh_app.mojo" [--android]
+devtools/common/mojo_run --embed https://core.mojoapps.io/ganesh_app.mojo [--android]
 ```
 
+By default, `mojo_run` uses https://core.mojoapps.io/kiosk_wm.mojo as the window
+manager. You can pass a different window manager url using the
+`--window-manager` flag to override this.
+
 For additional information on `mojo_run` refer to the built-in help and the
 [documentation](https://github.com/domokit/devtools/blob/master/README.md#runner).
 You can also request more information on what the tool is doing for you by
 passing the `--verbose` flag.
 
 ### <a name="debugging"></a>Debugging, tracing, profiling
 
 Devtools `mojo_debug` allows you to interactively inspect a running shell,
 collect performance traces and attach a gdb debugger.
 
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 running shell on the device) will not work unless the device is rooted and
 running a userdebug build. For Googlers, [follow the instructions at this
 link](http://go/mojo-internal-build-instructions).
 
 ### Running manually on Linux
 
 If you wish to, you can also run the Linux Mojo shell directly with no wrappers:
 ```
 ./out/Debug/mojo_shell out/Debug/spinning_cube.mojo
 ```