Add a warning if developers are not using JDK 8

Bug: 25786468
Change-Id: Ifaa782314d839079c17a572301550a0c2924f8c5
diff --git a/envsetup.sh b/envsetup.sh
index f266f1a..cb3dc10 100644
--- a/envsetup.sh
+++ b/envsetup.sh
@@ -1427,6 +1427,9 @@
 
     if [ ! "$JAVA_HOME" ]; then
       if [ ! "$EXPERIMENTAL_USE_JAVA8" ]; then
+        echo JDK 8 will soon become the default. Please install it now.
+        echo Also: \"export EXPERIMENTAL_USE_JAVA8=true\"
+        echo See http://go/android-jdk8-discuss
         case `uname -s` in
             Darwin)
                 export JAVA_HOME=$(/usr/libexec/java_home -v 1.7)