Merge "Enable Java language level 9 by default."

android/config.go

@@ -386,13 +386,14 @@ func NewConfig(srcDir, buildDir string) (Config, error) {
 
 func (c *config) fromEnv() error {
 	switch c.Getenv("EXPERIMENTAL_JAVA_LANGUAGE_LEVEL_9") {
-	case "":
-		// Nothing, this is the default
-	case "true":
-		// Use -source 9 -target 9
+	case "", "true":
+		// Use -source 9 -target 9. This is the default.
 		c.targetOpenJDK9 = true
+	case "false":
+		// Use -source 8 -target 8. This is the legacy behaviour.
+		c.targetOpenJDK9 = false
 	default:
-		return fmt.Errorf(`Invalid value for EXPERIMENTAL_JAVA_LANGUAGE_LEVEL_9, should be "" or "true"`)
+		return fmt.Errorf(`Invalid value for EXPERIMENTAL_JAVA_LANGUAGE_LEVEL_9, should be "", "true", or "false"`)
 	}
 
 	return nil