Silence generate_previous_version_mini_installer.py.

We only need to see the output from the alternate version generator
if something went wrong.  This stops a step from dumping a bunch of
output in the middle of `ninja -C out/Debug all`.

Bug: 918220
Change-Id: Iea15f70b354197d072a8b1ccee011b0ee40a01e1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2077283
Auto-Submit: Peter Kasting <pkasting@chromium.org>
Commit-Queue: Greg Thompson <grt@chromium.org>
Reviewed-by: Greg Thompson <grt@chromium.org>
Cr-Commit-Position: refs/heads/master@{#745023}

chrome/installer/mini_installer/generate_previous_version_mini_installer.py

@@ -22,14 +22,22 @@ def main():
   assert args.out
   assert args.path_7za
 
-  return subprocess.call([
-      args.alternate_version_generator,
-      '--force',
-      '--previous',
-      '--mini_installer=' + args.mini_installer,
-      '--out=' + args.out,
-      '--7za_path=' + args.path_7za,
-      ])
+  cmd = [args.alternate_version_generator,
+         '--force',
+         '--previous',
+         '--mini_installer=' + args.mini_installer,
+         '--out=' + args.out,
+         '--7za_path=' + args.path_7za,]
+
+  try:
+    # Run |cmd|, redirecting stderr to stdout in order for captured errors to be
+    # inline with corresponding stdout.
+    output = subprocess.check_output(cmd, stderr=subprocess.STDOUT)
+  except subprocess.CalledProcessError as e:
+    raise Exception("Error while running cmd: %s\n"
+                    "Exit code: %s\n"
+                    "Command output:\n%s" %
+                    (e.cmd, e.returncode, e.output))
 
 
 if '__main__' == __name__: