Add component build documentation.

docs/android_build_instructions.md

 # Android Build Instructions
 
 [TOC]
 
 ## Prerequisites
 
 A Linux build machine capable of building [Chrome for
 Linux](https://chromium.googlesource.com/chromium/src/+/master/docs/linux_build_instructions_prerequisites.md).
 Other (Mac/Windows) platforms are not supported for Android.
 
@@ skipping 34 matching lines @@
 [here](http://chromium-status.appspot.com/lkgr), and the last 100
 [here](http://chromium-status.appspot.com/revisions). Run:
 
 ```shell
 gclient sync --nohooks -r <lkgr-sha1>
 ```
 
 This is not needed for a typical developer workflow; only for one-time
 builds of Chromium.
 
-## Configure your build
+## Configure GN
 
-Android builds can be run with GN or GYP, though GN incremental builds
-are the fastest option and GN will soon be the only supported option.
-They are both meta-build systems that generate nina files for the
-Android build. Both builds are regularly tested on the build waterfall.
-
-### Configure GYP (deprecated -- use GN instead)
-
-If you are using GYP, next to the .gclient file, create a a file called
-'chromium.gyp_env' with the following contents:
-
-```shell
-echo "{ 'GYP_DEFINES': 'OS=android target_arch=arm', }" > chromium.gyp_env
-```
-
-Note that "arm" is the default architecture and can be omitted. If
-building for x86 or MIPS devices, change `target_arch` to "ia32" or
-"mipsel".
-
- **NOTE:** If you are using the `GYP_DEFINES` environment variable, it
-will override any settings in this file. Either clear it or set it to
-the values above before running `gclient runhooks`.
-
- See
-[build/android/developer\_recommended\_flags.gypi](https://code.google.com/p/chromium/codesearch#chromium/src/build/android/developer_recommended_flags.gypi&sq=package:chromium&type=cs&q=file:android/developer_recommended_flags.gypi&l=1)
-for other recommended GYP settings.
- Once chromium.gyp_env is ready, you need to run the following command
-to update projects from gyp files. You may need to run this again when
-you have added new files, updated gyp files, or sync'ed your
-repository.
-
-```shell
-gclient runhooks
-```
-
-#### This will download more things and prompt you to accept Terms of Service for Android SDK packages.
-
-## Configure GN (recommended)
-
-If you are using GN, create a build directory and set the build flags
-with:
+Create a build directory and set the build flags with:
 
 ```shell
 gn args out/Default
 ```
 
  You can replace out/Default with another name you choose inside the out
-directory. Do not use GYP's out/Debug or out/Release directories, as
-they may conflict with GYP builds.
+directory.
 
 Also be aware that some scripts (e.g. tombstones.py, adb_gdb.py)
 require you to set `CHROMIUM_OUTPUT_DIR=out/Default`.
 
 This command will bring up your editor with the GN build args. In this
 file add:
 
 ```
 target_os = "android"
 target_cpu = "arm"  # (default)
@@ skipping 69 matching lines @@
 
 ```shell
 third_party/android_tools/sdk/platform-tools/adb devices
 ```
 
 Which prints a list of connected devices. If not connected, try
 unplugging and reattaching your device.
 
 ### Build the full browser
 
-**Note: When adding new resource files or java files in gyp builds, you
-need to run 'gclient runhooks' again to get them in the build.**
-
 ```shell
 ninja -C out/Release chrome_public_apk
 ```
 
 And deploy it to your Android device:
 
 ```shell
-build/android/adb_install_apk.py out/Release/apks/ChromePublic.apk # For gyp.
 CHROMIUM_OUTPUT_DIR=$gndir build/android/adb_install_apk.py $gndir/apks/ChromePublic.apk # for gn.
 ```
 
 The app will appear on the device as "Chromium".
 
 ### Build Content shell
 
 Wraps the content module (but not the /chrome embedder). See
 [http://www.chromium.org/developers/content-module](http://www.chromium.org/developers/content-module)
 for details on the content module and content shell.
 
 ```shell
 ninja -C out/Release content_shell_apk
 build/android/adb_install_apk.py out/Release/apks/ContentShell.apk
 ```
 
 this will build and install an Android apk under
-`out/Release/apks/ContentShell.apk`. For GYP, replace `Release` with `Debug`
-above if you want to generate a Debug app. If you are using GN, substitute the
-name you initially gave to your build directory.
+`out/Release/apks/ContentShell.apk`. (Where `Release` is the name of your build
+directory.)
 
 If you use custom out dir instead of standard out/ dir, use
 CHROMIUM_OUT_DIR env.
 
 ```shell
 export CHROMIUM_OUT_DIR=out_android
 ```
 
 ### Build WebView shell
 
@@ skipping 112 matching lines @@
 release of Chrome for Android (v25+) you can do the following steps.
 Note that in order to get your changes into the official release, you'll
 need to send your change for a codereview using the regular process for
 committing code to chromium.
 
 1.  Open Chrome on your Android device and visit chrome://version
 2.  Copy down the id listed next to "Build ID:"
 3.  Go to
     [http://storage.googleapis.com/chrome-browser-components/BUILD\_ID\_FROM\_STEP\_2/index.html](http://storage.googleapis.com/chrome-browser-components/BUILD_ID_FROM_STEP_2/index.html)
 4.  Download the listed files and follow the steps in the README.