Add android_ninja, like android_make for ninja.

Add android_ninja, like android_make for ninja.

android_ninja {tests,bench,gm,bench_pictures,render_pictures} all build and run
fine.  They build so fast I thought maybe they were broken.

Note that android_ninja with no argument is failing:
    ninja: Entering directory `out/config/android-arm_v7_thumb/Debug'
    ninja: error: 'lib.target/libSampleApp.so', needed by 'android/libs/armeabi-v7a/libSampleApp.so', missing and no known rule to make it
Will look into this.

BUG=
R=djsollen@google.com

Committed: https://code.google.com/p/skia/source/detail?r=11525

Review URL: https://codereview.chromium.org/24833002

git-svn-id: http://skia.googlecode.com/svn/trunk@11527 2bbb7eff-a529-9590-31e7-b0007b416f81