Improve Android Quick Start Guide

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._
 
 The following libraries/utilities are required in addition to those needed for a standard skia checkout:
 
   * The Android SDK: http://developer.android.com/sdk/
 
 Check out the source code
 -------------------------
 
 Follow the instructions [here](../download) for downloading the Skia source. 
 
 Inside your Skia checkout, `platform_tools/android` contains the Android setup
 scripts, Android specific dependencies, and the Android Sample App.
 
 You may need to [install other dependencies](./linux#prerequisites):
 
     tools/install_dependencies.sh
+    bin/sync-and-gyp

[djsollen, 2016/04/25 18:35:16]

I'll upload a CL to make this a little more clear as you'll need to run this
step anytime you sync the source code.

[liyuqian, 2016/04/25 19:10:11]

Done.

 
 Setup the Android SDK
 ---------------------
 
 To finish setting up the Android SDK you need to download use the SDK to
 download the appropriate API level.  To do this simply go to the directory
 where you installed the SDK and run the following commands
 
     # You may want to add this export to your shell's .bash_profile or .profile
     export ANDROID_SDK_ROOT=/path/to/android/sdk
@@ skipping 13 matching lines @@
 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.
 
 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).
+ninja (see descriptions of some of the other flags here). Please make sure
+that Android SDK Build-tools 22.0.1 is installed.

[djsollen, 2016/04/25 18:35:16]

move this to the "setup the android sdk" section and in its own paragraph
provide details for how to do it (like in your doc).

[liyuqian, 2016/04/25 19:10:11]

Done.

 
     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
@@ skipping 128 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.