depot_tools: Use gclient_utils.AskForData instead of raw_input.

gclient_utils.AskForData will use raw_input on Python 2 and input on Python 3.

Bug: 1063976
Change-Id: I93c059c4e4454d01787716b5a0a2641ad5253f53
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2116370
Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>
Reviewed-by: Anthony Polito <apolito@google.com>
Auto-Submit: Edward Lesmes <ehmaldonado@chromium.org>
diff --git a/git_nav_downstream.py b/git_nav_downstream.py
index 2d2287c..1eeeb6a 100755
--- a/git_nav_downstream.py
+++ b/git_nav_downstream.py
@@ -14,6 +14,7 @@
 import argparse
 import sys
 
+import gclient_utils
 from git_common import current_branch, branches, upstream, run, hash_one
 import metrics
 
@@ -53,7 +54,7 @@
       if r:
         print(prompt + r)
       else:
-        r = raw_input(prompt).strip() or '0'
+        r = gclient_utils.AskForData(prompt).strip() or '0'
       if not r.isdigit() or (0 > int(r) > high):
         print("Invalid choice.")
       else: