Update the build instructions to be consistent.

docs/android_build_instructions.md

 # Android Build Instructions
 
+**See also [the old version of this page](old_android_build_instructions.md).**
+
+Google employee? See [go/building-chrome](https://goto.google.com/building-chrome) instead.
+
 [TOC]
 
-## Prerequisites
+## System requirements
 
-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.
+* A 64-bit Intel machine running Linux with at least 8GB of RAM. More
+  than 16GB is highly recommended.
+* At least 100GB of free disk space.
+* You must have Git and Python installed already.
 
-## Getting the code
+Most development is done on Ubuntu. Other distros may or may not work;
+see the [linux instructions](linux_build_instructions.md) for some suggestions.
 
-First, check out and install the [depot\_tools
-package](https://commondatastorage.googleapis.com/chrome-infra-docs/flat/depot_tools/docs/html/depot_tools_tutorial.html#_setting_up).
+Building the Android client on Windows or Mac is not supported and doesn't work.
 
-Then, if you have no existing checkout, create your source directory and
-get the code:
+## Install `depot_tools`
 
-```shell
-mkdir ~/chromium && cd ~/chromium
-fetch --nohooks android # This will take 30 minutes on a fast connection
-```
+Clone the depot_tools repository:
+
+    $ git clone https://chromium.googlesource.com/chromium/tools/depot_tools.git
+
+Add depot_tools to the end of your PATH (you will probably want to put this
+in your ~/.bashrc or ~/.zshrc). Assuming you cloned depot_tools
+to /path/to/depot_tools:
+
+    $ export PATH=$PATH:/path/to/depot_tools
+
+## Get the code
+
+Create a chromium directory for the checkout and change to it (you can call
+this whatever you like and put it wherever you like, as
+long as the full path has no spaces):
+
+    $ mkdir ~/chromium && cd ~/chromium
+    $ fetch --nohooks android
+
+If you don't want the full repo history, you can save a lot of time by
+adding the `--no-history` flag to fetch.
+
+Expect the command to take 30 minutes on even a fast connection, and many
+hours on slower ones.
+
+If you've already installed the build dependencies on the machine (from another
+checkout, for example), you can omit the `--nohooks` flag and fetch
+will automatically execute `gclient runhooks` at the end.
+
+When fetch completes, it will have created a directory called `src`.
+The remaining instructions assume you are now in that directory:
+
+    $ cd src
+
+### Converting an existing Linux checkout
 
 If you have an existing Linux checkout, you can add Android support by
 appending `target_os = ['android']` to your .gclient file (in the
 directory above src):
 
-```shell
-cat > .gclient <<EOF
- solutions = [ ...existing stuff in here... ]
- target_os = [ 'android' ] # Add this to get Android stuff checked out.
-EOF
-```
+    $ echo "target_os = [ 'android' ]" >> ../.gclient
 
-Then run gclient sync to get the Android stuff checked out:
+Then run gclient sync to pull the new Android dependencies:
 
-```shell
-gclient sync
-```
+    gclient sync
 
-## (Optional) Check out LKGR
+(This is actually the difference between `fetch android` and `fetch chromium`).
 
-If you want a single build of Chromium in a known good state, sync to
-the LKGR ("last known good revision"). You can find it
-[here](http://chromium-status.appspot.com/lkgr), and the last 100
-[here](http://chromium-status.appspot.com/revisions). Run:
+### Install additional build dependencies
 
-```shell
-gclient sync --nohooks -r <lkgr-sha1>
-```
+Once you have checked out the code, run
 
-This is not needed for a typical developer workflow; only for one-time
-builds of Chromium.
+    build/install-build-deps-android.sh
 
-## Configure GN
+to get all of the dependencies you need to build on Linux *plus* all of the
+Android-specific dependencies (you need some of the regular Linux dependencies
+because an Android build builds a bunch of the Linux tools and utilities).
 
-Create a build directory and set the build flags with:
+### Run the hooks
 
-```shell
-gn args out/Default
-```
+Once you've run `install-build-deps` at least once, you can now run the
+chromium-specific hooks, which will download additional binaries and other
+things you might need:
 
- You can replace out/Default with another name you choose inside the out
-directory.
+    $ gclient runhooks
 
-Also be aware that some scripts (e.g. tombstones.py, adb_gdb.py)
-require you to set `CHROMIUM_OUTPUT_DIR=out/Default`.
+*Optional*: You can also [install API keys](https://www.chromium.org/developers/how-tos/api-keys)
+if you want to talk to some of the Google services, but this is not necessary
+for most development and testing purposes.
 
-This command will bring up your editor with the GN build args. In this
-file add:
-
-```
-target_os = "android"
-target_cpu = "arm"  # (default)
-is_debug = true  # (default)
-
-# Other args you may want to set:
-is_component_build = true
-is_clang = true
-symbol_level = 1  # Faster build with fewer symbols. -g1 rather than -g2
-enable_incremental_javac = true  # Much faster; experimental
-```
-
-You can also specify `target_cpu` values of "x86" and "mipsel". Re-run
-gn args on that directory to edit the flags in the future. See the [GN
-build
-configuration](https://www.chromium.org/developers/gn-build-configuration)
-page for other flags you may want to set.
-
-### Install build dependencies
-
-Update the system packages required to build by running:
-
-```shell
-./build/install-build-deps-android.sh
-```
+### Configure the JDK
 
 Make also sure that OpenJDK 1.7 is selected as default:
 
 `sudo update-alternatives --config javac`
 `sudo update-alternatives --config java`
 `sudo update-alternatives --config javaws`
 `sudo update-alternatives --config javap`
 `sudo update-alternatives --config jar`
 `sudo update-alternatives --config jarsigner`
 
-### Synchronize sub-directories.
+## Setting up the Build
 
-```shell
-gclient sync
-```
+Chromium uses [Ninja](https://ninja-build.org) as its main build tool, and
+a tool called [GN](../tools/gn/docs/quick_start.md) to generate
+the .ninja files to do the build. To create a build directory configured
+to build Android, run:
 
-## Build and install the APKs
+    $ gn gen '--args="target_os="android"' out/Default
+
+* You only have to do run this command once, it will self-update the build
+  files as needed after that.
+* You can replace `out/Default` with another directory name, but we recommend
+  it should still be a subdirectory of `out`.
+* To specify build parameters for GN builds, including release settings,
+  see [GN build configuration](https://www.chromium.org/developers/gn-build-configuration). 
+  The default will be a debug component build matching the current host
+  operating system and CPU.
+* For more info on GN, run `gn help` on the command line or read the
+  [quick start guide](../tools/gn/docs/quick_start.md).
+
+Also be aware that some scripts (e.g. tombstones.py, adb_gdb.py)
+require you to set `CHROMIUM_OUTPUT_DIR=out/Default`.
+
+## Build Chromium
+
+Build Chromium with Ninja using the command:
+
+    $ ninja -C out/Default chrome_public_apk
+
+You can get a list of all of the other build targets from GN by running
+`gn ls out/Default` from the command line. To compile one, pass to Ninja
+the GN label with no preceding "//" (so for `//chrome/test:unit_tests`
+use ninja -C out/Default chrome/test:unit_tests`).
+## Installing and Running Chromium on a device
 
 If the `adb_install_apk.py` script below fails, make sure aapt is in
 your PATH. If not, add aapt's path to your PATH environment variable (it
 should be
 `/path/to/src/third_party/android_tools/sdk/build-tools/{latest_version}/`).
 
 Prepare the environment:
 
 ```shell
 . build/android/envsetup.sh
@@ skipping 159 matching lines @@
 ninja -C out/Default chrome_public_test_apk_incremental
 out/Default/bin/run_chrome_public_test_apk_incremental
 ```
 
 To uninstall:
 
 ```shell
 out/Default/bin/install_chrome_public_apk_incremental -v --uninstall
 ```
 
-### Miscellaneous
+## Tips, tricks, and troubleshooting
 
-#### Rebuilding libchrome.so for a particular release
+### Rebuilding libchrome.so for a particular release
 
 These instructions are only necessary for Chrome 51 and earlier.
 
 In the case where you want to modify the native code for an existing
 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.