In my Android Studio 3.0.1 installation, the buttons you seek are already in the main toolbar (see where the red arrow points):
To configure the contents of the toolbars, right-click over an open area in the toolbar panel and choose “Customize Menus and Toolbars…” from the context menu:
That will bring up a dialog where you can see the contents of the main toolbar and manipulate those contents:
In Android Studio 3.3 Canary 13:
Open View and then click Toolbar if it is unchecked. You will now get your toolbar with back and forward navigate buttons.
Best of Luck!