Update android docs for how to sync source code

site/user/quick/android.md

 Android
 =======
 
 Prerequisites
 -------------
 
 _Currently we only support building Skia for Android on a Linux or Mac host! In addition,
  we only use the Mac build for local development. All shipping variants are compiled on
  Linux for performance reasons._
 
@@ skipping 31 matching lines @@
 many other Android add-ons or APIs as you want, but you only are required to
 have this one in order to complete the Skia build process.
 
 Setup Environment for Android
 -----------------------------
 
 The Android build needs to set up some specific variables needed by both GYP
 and Make. We make this setup easy for developers by encapsulating all the
 details into a custom script that acts as a replacement for make.
 
+Syncing the Source
+-----------------------------
+We use the gclient utility, provided by depot_tools, to sync both our git repository
+as well as any third-party dependencies.  If you are an expert user you can setup
+a .gclient file on your own, but for everyone else it is recommended that you use
+`bin/sync-and-gyp` to create a .gclient file for the first time.
+
+After the initial setup you only need to run `gclient sync` to get the latest
+sources.
+
+Further, we use the open-source gyp tool to generate build files from our
+multi-platform "gyp" files. While most other platforms encourage you to
+regenerate these files using `./gyp_skia` or `bin/sync-and-gyp` it is
+recommended that you do NOT do this for Android.  Instead you can rely
+on it being run automatically by android_ninja.

[scroggo, 2016/04/25 19:02:05]

It's weird that we have a different process here. I'm guessing that
android_ninja supplies options to gyp_skia, so running sync-and-gyp or gyp_skia
will use the default options, which will be overwritten?

FWIW, it seems like the bad way is not that bad - it just means doing some
wasted work. (And I believe gyp_skia is fairly fast.) Or is there some harm to
running gyp_skia?

+
 Custom Android Build Script
 ---------------------------
 
 The android_ninja script is a wrapper for the ninja command (provided by
 depot_tools) and is specifically designed to work with the Skia's build
 system. To use the script you need to call it from Skia's trunk directory with
 the -d option plus any of the options or arguments you would normally pass to
 ninja (see descriptions of some of the other flags here).
 
     export ANDROID_SDK_ROOT=/path/to/android/sdk
     export ANDROID_HOME=/path/to/android/sdk
     export PATH=$PATH:/path/to/depot_tools
 
     cd skia
     ./platform_tools/android/bin/android_ninja -d nexus_10 # or nexus_7, galaxy_nexus, etc...
 
 The -d option enables the build system to target the build to a specific
 architecture such as MIPS (generic), x86 (generic) and ARM (generic and device
 specific flavors for Nexus devices). This in turn allows Skia to take
 advantage of specific device optimizations (e.g. NEON instructions).
 
-Generate build file from GYP
-----------------------------
-
-We use the open-source gyp tool to generate build files from our
-multi-platform "gyp" files. While most other platforms enable you to
-regenerate these files using `./gyp_skia` or `bin/sync-and-gyp` it is
-recommended that you do NOT do this for Android.  Instead you can rely
-on it being run automatically by android_ninja.
-
 Faster rebuilds
 ---------------
 
 You can use ccache to improve the speed of rebuilding:
 
     # You may want to add this export to your shell's .bash_profile or .profile
     export ANDROID_MAKE_CCACHE=[ccache]
 
 Build and run executables on the device
 ---------------------------------------
@@ skipping 106 matching lines @@
     # COMMAND LINE APPS
     # include additional arguments in quotes (e.g. "dm --nopdf")
     ./platform_tools/android/bin/android_gdb_native dm
     
     # SAMPLE APP
     # make sure you've installed the app on the device first
     ./platform_tools/android/bin/android_gdb_app [-d device_id]
 
 When the gdb client is ready, insert a breakpoint, and continue to let the
 program resume execution.