Add a helper script to expose which version of adb the android scripts use.

Review URL: https://codereview.chromium.org/692633002

platform_tools/android/bin/adb_print_path

@@ -0,0 +1,12 @@
+#!/bin/bash
+#
+# adb_print_path: prints the path to the copy of adb that will be used by Skia's
+# android scripts. This is used by Skia's build infrastructure to ensure that
+# we use the same adb revision (and instance). 
+
+SCRIPT_DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )"
+source $SCRIPT_DIR/android_setup.sh
+source $SCRIPT_DIR/utils/setup_adb.sh
+
+echo $ADB
+exit 0