Fix PROGRAM_FILES substitutions when running in x64 builds of Python.

Chrome is unconditionally installed in "Program Files (x86)".

BUG=763606

Change-Id: I5c4d81c34a166f61969e0698536636e5bcb6bbf9
Reviewed-on: https://chromium-review.googlesource.com/663257
Commit-Queue: Gabriel Charette <gab@chromium.org>
Reviewed-by: Gabriel Charette <gab@chromium.org>
Cr-Commit-Position: refs/heads/master@{#501417}

chrome/test/mini_installer/variable_expander.py

@@ -119,7 +119,8 @@ class VariableExpander:
         'NEXT_VERSION_MINI_INSTALLER': next_version_mini_installer_abspath,
         'NEXT_VERSION_MINI_INSTALLER_FILE_VERSION': _GetFileVersion(
             next_version_mini_installer_abspath),
-        'PROGRAM_FILES': shell.SHGetFolderPath(0, shellcon.CSIDL_PROGRAM_FILES,
+        'PROGRAM_FILES': shell.SHGetFolderPath(0,
+                                               shellcon.CSIDL_PROGRAM_FILESX86,
                                                None, 0),
         'USER_SPECIFIC_REGISTRY_SUFFIX': _GetUserSpecificRegistrySuffix(),
         'VERSION_SERVER_2003': '(5, 2)',