It appears that Microsoft is in the process of integrating Gmail, Google Drive, and Google Calendar with its own webmail client, Outlook.com. A user reports that it is possible to add a Gmail account to Outlook.com.
Windows user Florian B posts to Twitter a screenshot of Outlook showing that Gmail and the Google calendar can be added to Outlook, so that everything can be managed from one place. Linking a Google account to an Outlook.com account makes Gmail, Drive documents, and the calendar visible in the Outlook web client inbox. The integration is similar to the Outlook apps for Android and iOS.
The integration of Gmail and Outlook is according to Florian still in an early phase, because it is not yet possible, for example, to switch easily between the two; the whole page then loads over and over again according to him. Also, it would not be possible to add more than one Google account. Based on this, it seems to be a test for the time being, although it is also possible that the integration is part of a phased implementation.
It is unknown when this integration will be available to all users. Microsoft has not released any official information about this yet.