Google Search uses Chrome Custom Tabs since April 27, 2016. From 9to5Google,
After its most recent update, the Google app now opens search results as Chrome Custom Tabs. [...]
[...]. By default, links from search results now open as a Custom Tab that features a blue action bar with options to Share, Copy link, Find in page, and Open in Chrome.
To change its behavior, open Google app's setting by e.g. tapping Google app from app launcher to navigate to Google Now screen, tap hamburger icon (3 horizontal bars) on top-left to open navigation drawer, then,
Users can go to Settings > Accounts & privacy to toggle off the new ‘Open web pages in app' option if they prefer opening all links the old way.
Related: Prevent apps opening links in Chrome Custom Tabs (i.e. open in default browser directly)