Update the build instructions to be consistent.

docs/chromeos_build_instructions.md

-# ChromeOS Build Instructions (Chromium OS on Linux)
-
-Chromium on Chromium OS is built from a mix of code sourced from Chromium
-on Linux and Chromium on Windows. Much of the user interface code is
-shared with Chromium on Windows.
-
-If you make changes to Chromium on Windows, they may affect Chromium
-on Chromium OS. Fortunately to test the effects of your changes you
-don't need to build all of Chromium OS, you can just build Chromium for
-Chromium OS directly on Linux.
-
-First, follow the [normal Linux build
-instructions](https://chromium.googlesource.com/chromium/src/+/master/docs/linux_build_instructions.md)
-as usual to get a Chromium checkout.
-
-## Building and running Chromium with Chromium OS UI on your local machine
-
-If you plan to test the Chromium build on your dev machine and not a
-Chromium OS device, run the following in your chromium checkout:
-
-    $ gn gen out/Default --args='target_os="chromeos"'
-    $ ninja -C out/Default
-
-NOTE: You may wish to replace 'Default' with something like 'Cros' if
-you switch back and forth between Linux and Chromium OS builds, or 'Debug'
-if you want to differentiate between Debug and Release builds (see below)
-or DebugCros or whatever you like.
-
-Now, when you build, you will build with Chromium OS features turned on.
-
-See [GN Build Configuration](https://www.chromium.org/developers/gn-build-configuration)
-for more information about configuring your build.
-
-If you have not already done so, be sure to set the following to prevent
-'gclient runhooks' from executing 'gyp_chromium':
-
-    export GYP_CHROMIUM_NO_ACTION=1
-
-Some additional options you may wish to set by passing in **--args** to
-**gn gen** or running **gn args out/Default**:
-
-    is_component_build = true
-    use_goma = true
-    is_debug = false  # Release build
-    dcheck_always_on = true  # Enable DCHECK (with is_debug = false)
-    is_official_build = true
-    is_chrome_branded = true
-
-## Notes
-
-When you build Chromium OS Chromium, you'll be using the TOOLKIT\_VIEWS
-front-end just like Windows, so the files you'll probably want are in
-src/ui/views and src/chrome/browser/ui/views.
-
-When target_os = "chromeos", then toolkit\_views need not (and should not)
-be specified.
-
-The Chromium OS build requires a functioning GL so if you plan on
-testing it through Chromium Remote Desktop you might face drawing
-problems (e.g. Aura window not painting anything). Possible remedies:
-
-*   --ui-enable-software-compositing --ui-disable-threaded-compositing
-*   --use-gl=osmesa, but it's ultra slow, and you'll have to build
-    osmesa yourself.
-*   ... or just don't use Remote Desktop. :)
-
-To more closely match the UI used on devices, you can install fonts used
-by Chrome OS, such as Roboto, on your Linux distro.
-
-To specify a logged in user:
-
-*   For first run, add the following options to the command line:
-    **--user-data-dir=/tmp/chrome --login-manager**
-*   Go through the out-of-the-box UX and sign in as
-    **username@gmail.com**
-*   For subsequent runs, add the following to the command line:
-    **--user-data-dir=/tmp/chrome --login-user=username@gmail.com**.
-*   To run in guest mode instantly, you can run add the arguments
-    **--user-data-dir=/tmp/chrome --bwsi --incognito
-    --login-user='$guest' --login-profile=user**
-
-Signing in as a specific user is useful for debugging features like sync
-that require a logged in user.
-
-## Compile Chromium for a Chromium OS device using the Chromium OS SDK
-
-See [Building Chromium for a Chromium OS device](https://www.chromium.org/chromium-os/how-tos-and-troubleshooting/building-chromium-browser)
-for information about building and testing chromium for Chromium OS.