Last year, Google launched the ability to see results from your Gmail, Google Drive and Google Calendar accounts as you type in the search box from Gmail. This was only available as part of a field trial.
Soon, all users in the U.S. will be getting this functionality. Google software engineer Balazs Racz says in a brief blog post:
As part of field trial we opened in October, it became possible to instantly see your relevant emails, Google Drive files, Calendar events, and more when you search in Gmail. Those of you who participated in the field trial told us that you like the time-saving convenience of searching for all your stuff from one place, and over the coming week, we'll be rolling out this feature in English to all U.S. users. Now you can find what you're looking for faster right in Gmail.
The feature is nice, but the part of the field trial that lets users retrieve content from Gmail, Google Drive and Google Calendar when searching Google's regular web search is even better. It remains to be seen when this functionality will become available to all.