Introduce the --sdk-build flag for Android's native test generator

This flag supersedes --ant-compile and takes its value from gyp's sdk_build
variable. It will tell the native test generator script to use Ant for Java
compilation (default) instead of the Android.mk file.
    
BUG=
TEST=

Review URL: https://chromiumcodereview.appspot.com/10821128

git-svn-id: http://src.chromium.org/svn/trunk/src/build@149440 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

apk_test.gypi

@@ -47,7 +47,7 @@
               '<(android_app_abi)',
               '--ant-args',
               '-DPRODUCT_DIR=<(ant_build_out)',
-              '--ant-compile'
+              '--sdk-build=<(sdk_build)',
             ],
           }],
         }],  # 'OS == "android" and gtest_target_type == "shared_library"