autoninja: Don't echo command-line unless NINJA_SUMMARIZE_BUILD=1

I want to use autoninja from //build/android/generate_gradle.py, but I
invoke it with a *long* list of targets that I do not want echo'ed

Bug: 803493
Change-Id: I98ad85b64ec7ce60b7e3df9827fb613cd57638e5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1596535Reviewed-by: Bruce Dawson <brucedawson@chromium.org>
Commit-Queue: Andrew Grieve <agrieve@chromium.org>

autoninja

@@ -11,7 +11,9 @@ export AUTONINJA_BUILD_ID
 # Execute whatever is printed by autoninja.py.
 # Also print it to reassure that the right settings are being used.
 command=$(python "$(dirname -- "$0")/autoninja.py" "$@")
-echo "$command"
+if [ "$NINJA_SUMMARIZE_BUILD" == "1" ]; then
+  echo "$command"
+fi
 if eval "$command"; then
   if [ "$NINJA_SUMMARIZE_BUILD" == "1" ]; then
     python "$(dirname -- "$0")/post_build_ninja_summary.py" "$@"