Improve error message in case of resource ID collision

Change-Id: Id4a2a9b4b20d6f6c243340159925474eacc5fe6d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2558404Reviewed-by: dpapad <dpapad@chromium.org>
Commit-Queue: dpapad <dpapad@chromium.org>
Auto-Submit: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#830964}

tools/grit/grit/format/data_pack.py

@@ -283,7 +283,10 @@ def RePackFromDataPackStrings(inputs,
     # Make sure we have no dups.
     duplicate_keys = set(input_resources.keys()) & set(resources.keys())
     if duplicate_keys:
-      raise KeyError('Duplicate keys: ' + str(list(duplicate_keys)))
+      raise KeyError(
+        'Duplicate resource IDs: ' + str(list(duplicate_keys)) + '. '
+        'This is likely because the reserved ID ranges defined in' +
+        'tools/gritsettings/resource_ids.spec have been exhausted.')
 
     # Make sure encoding is consistent.
     if encoding in (None, BINARY):