Added assertion message when ATL is not installed.

The comment above assert did not match behavior
of assert. This comment has been fixed and an
explanatory assertion message was added.

Bug: None
Change-Id: If9ac26c578ac45fb9e6dd50b1605ecff13bf1323
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1881161Reviewed-by: Bruce Dawson <brucedawson@chromium.org>
Commit-Queue: Yura Yaroshevich <yura.yaroshevich@gmail.com>
Cr-Commit-Position: refs/heads/master@{#710425}

build/toolchain/win/setup_toolchain.py

@@ -280,8 +280,10 @@ def main():
   assert vc_lib_path
   print('vc_lib_path = ' + gn_helpers.ToGNString(vc_lib_path))
   if (target_store != True):
-    # Path is assumed not to exist for desktop applications
-    assert vc_lib_atlmfc_path
+    # Path is assumed to exist for desktop applications
+    assert (vc_lib_atlmfc_path,
+            "Microsoft.VisualStudio.Component.VC.ATLMFC is not found, " +
+            "check if it's installed.")
   # Possible atlmfc library path gets introduced in the future for store thus
   # output result if a result exists.
   if (vc_lib_atlmfc_path != ''):