Add testing subcommand to fasta tool.

pkg/front_end/tool/fasta

Index: pkg/front_end/tool/fasta
diff --git a/pkg/front_end/tool/fasta b/pkg/front_end/tool/fasta
index a82ad51997cfb3dbda187f8e11e8ee13684b2c19..aa43e71aaa89ee847869bec3db411e1681f0014c 100755
--- a/pkg/front_end/tool/fasta
+++ b/pkg/front_end/tool/fasta
@@ -47,6 +47,10 @@ case "${1//_/-}" in
       stop "Usage: $1 dillfile [output]"
     fi
     ;;
+  testing)
+    SCRIPT="${REPO_DIR}/pkg/testing/bin/testing.dart"
+    set -- "$@" "--config=${REPO_DIR}/pkg/front_end/test/fasta/testing.json"
+    ;;
   *)
     stop "'$1' isn't a valid subcommand."
     ;;
@@ -54,4 +58,4 @@ esac
 
 shift
 
-exec "${DART_VM}" -c "${SCRIPT}" "$@"
+DART_CONFIGURATION=${DART_CONFIGURATION:-ReleaseX64} exec "${DART_VM}" -c "${SCRIPT}" "$@"