Custom Gradle home and add .vpython file (flutter#20425)

Author: Emmanuel Garcia

testing/scenario_app/.gitignore

@@ -5,3 +5,6 @@ build/
 ios/Scenarios/*.framework/
 android/app/libs/flutter.jar
 android/app/src/main/jniLibs/arm64-v8a/libapp.so
+android/gradle-home/.cache
+
+!.vpython

testing/scenario_app/README.md

@@ -48,6 +48,7 @@ The test is run on a x86 emulator. To run the test locally, you must create an e
 hw.lcd.density = 480
 hw.lcd.height = 1920
 hw.lcd.width = 1080
+lcd.depth = 16
 ```
 
 This file is typically located in your `$HOME/.android/avd/<avd>` folder.

testing/scenario_app/android/gradle-home/.vpython

@@ -0,0 +1,11 @@
+#
+# "vpython" specification file for build
+#
+# Pillow is required by com.facebook.testing.screenshot.
+
+python_version: "2.7"
+
+wheel: <
+  name: "infra/python/wheels/pillow/${vpython_platform}"
+  version: "version:6.0.0"
+>

testing/scenario_app/android/gradle-home/bin/python

@@ -0,0 +1,14 @@
+#!/bin/bash
+
+# This script is added to the PATH on LUCI when executing the junit tests.
+# The Python scripts used to compare the screenshots are contained in a jar file.
+# As a result, vpython cannot find the .vpython spec file because it's outside
+# of the jar file.
+
+set -e
+
+SCRIPT_DIR="$( dirname "${BASH_SOURCE[0]}" )"
+
+echo "Running from $SCRIPT_DIR/bin/python"
+
+vpython -vpython-spec "$SCRIPT_DIR/../.vpython" "$@"