Convert print statements to Python 3 style

Ran "2to3 -w -n -f print ./" and manually added imports.
Ran "^\s*print " and "\s+print " to find batch/shell scripts, comments and the like with embedded code, and updated them manually.
Also manually added imports to files, which used print as a function, but were missing the import.

The scripts still work with Python 2.
There are no intended behaviour changes.

Bug: 942522
Change-Id: Id777e4d4df4adcdfdab1b18bde89f235ef491b9f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/1595684
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Commit-Queue: Dirk Pranke <dpranke@chromium.org>
Auto-Submit: Raul Tambre <raul@tambre.ee>

git_nav_downstream.py

@@ -9,6 +9,8 @@ is more than one downstream branch, then this script will prompt you to select
 which branch.
 """
 
+from __future__ import print_function
+
 import argparse
 import sys
 
@@ -36,24 +38,24 @@ def main(args):
     cur = hash_one(cur)
   downstreams = [b for b in branches() if upfn(b) == cur]
   if not downstreams:
-    print "No downstream branches"
+    print("No downstream branches")
     return 1
   elif len(downstreams) == 1:
     run('checkout', downstreams[0], stdout=sys.stdout, stderr=sys.stderr)
   else:
     high = len(downstreams) - 1
     while True:
-      print "Please select a downstream branch"
+      print("Please select a downstream branch")
       for i, b in enumerate(downstreams):
-        print "  %d. %s" % (i, b)
+        print("  %d. %s" % (i, b))
       prompt = "Selection (0-%d)[0]: " % high
       r = opts.pick
       if r:
-        print prompt + r
+        print(prompt + r)
       else:
         r = raw_input(prompt).strip() or '0'
       if not r.isdigit() or (0 > int(r) > high):
-        print "Invalid choice."
+        print("Invalid choice.")
       else:
         run('checkout', downstreams[int(r)], stdout=sys.stdout,
             stderr=sys.stderr)