Reland "Add JAVA_HOME to environment to ensure always compiling with JDK 8"

This reverts commit 8a42f7fcee668c55f7b89593076614befd178918.

Change-Id: Iea4cf97ee23aab7b9541d4cb684ce31f0cc85107
diff --git a/tools/jdk.py b/tools/jdk.py
index 5791e50..bc40873 100755
--- a/tools/jdk.py
+++ b/tools/jdk.py
@@ -20,6 +20,15 @@
   else:
     return os.environ['JAVA_HOME']
 
+def GetJdk8Home():
+  root = os.path.join(JDK_DIR, 'jdk8')
+  if defines.IsLinux():
+    return os.path.join(root, 'linux-x86')
+  elif defines.IsOsX():
+    return os.path.join(root, 'darwin-x86')
+  else:
+    return os.environ['JAVA_HOME']
+
 def GetJavaExecutable(jdkHome=None):
   jdkHome = jdkHome if jdkHome else GetJdkHome()
   executable = 'java.exe' if defines.IsWindows() else 'java'
diff --git a/tools/run_on_as_app.py b/tools/run_on_as_app.py
index fbe4069..42b7cae 100755
--- a/tools/run_on_as_app.py
+++ b/tools/run_on_as_app.py
@@ -719,6 +719,7 @@
       app, checkout_dir, proguard_config_dest)
 
   env_vars = {}
+  env_vars['JAVA_HOME'] = jdk.GetJdk8Home()
   env_vars['ANDROID_HOME'] = utils.getAndroidHome()
   if not options.disable_assertions:
     env_vars['JAVA_OPTS'] = '-ea:com.android.tools.r8...'