We recently noticed that on ChromeOS, there are two values being logged for the Extensions.ExtensionLoad histogram, one of them with a count of zero extensions. It appears that this has something to do with the Off The Record profile that ChromeOS uses to implement their signin page. This is a problem because we generally use this data to reason about things like "number of extensions users have installed at browser startup", and the presence of a bunch of 0-count entries makes this harder to do. 

The specific problem happens because ExtensionService::Init gets called for both the normal profile and the signin "pseudo" profile, and in both cases we end up calling into InstalledLoader::RecordExtensionsMetrics().