[Zucchini] Upload debug symbols to unsigned staging

In order to better debug any crashes of zucchini.exe this change adds
debug symbols to the Chrome symbols archive on unsigned staging.

Bug: 729154
Change-Id: I6ece17e8bedcb53801dc9f3e981d92186a759314
Reviewed-on: https://chromium-review.googlesource.com/940083Reviewed-by: Greg Thompson <grt@chromium.org>
Commit-Queue: Calder Kitagawa <ckitagawa@google.com>
Cr-Commit-Position: refs/heads/master@{#539855}

chrome/tools/build/win/FILES.cfg

@@ -662,6 +662,12 @@ FILES = [
     'optional': ['official'],
     'archive': 'zucchini.exe',
   },
+  {
+    'filename': 'zucchini.exe.pdb',
+    'buildtype': ['official'],
+    'optional': ['official'],
+    'archive': 'chrome-win32-syms.zip',
+  },
   {
     'filename': 'chrome.dll.pdb',
     'buildtype': ['dev', 'official'],