Add a prompt to try out RBE for local builds

This is to nudge developers to use RBE especially when they run into
long builds and do NOT have RBE turned on.

Change-Id: I7da94763f5387310e522931bf650f9d7c01dc7f2

envsetup.sh

@@ -1661,12 +1661,19 @@ function _wrap_build()
     if [ -n "$ncolors" ] && [ $ncolors -ge 8 ]; then
         color_failed=$'\E'"[0;31m"
         color_success=$'\E'"[0;32m"
+        color_warning=$'\E'"[0;33m"
         color_reset=$'\E'"[00m"
     else
         color_failed=""
         color_success=""
         color_reset=""
     fi
+
+    if [[ "x${USE_RBE}" == "x" && $mins -gt 15 && "${ANDROID_BUILD_ENVIRONMENT_CONFIG}" == "googler" ]]; then
+        echo
+        echo "${color_warning}Start using RBE (http://go/build-fast) to get faster builds!${color_reset}"
+    fi
+
     echo
     if [ $ret -eq 0 ] ; then
         echo -n "${color_success}#### build completed successfully "