Google is implementing material design for Chrome PDF Viewer right now, you can test it by running Chrome Canary with the –enable-pdf-material-ui switch and try open any PDF in the Chrome browser -ensure Chrome PDF Viewer plugin is enabled in about:plugins page before that.

From the screenshot below you can see toolbar only offers save and print buttons, soon bookmarks, Zoom and Go to page feature buttons will be added to it.

Chrome PDF Viewer with material design UI

Check this bug for more details.

Update: Bookmarks’ button has been added to the toolbar, which when you click opens a pane on right-side in Chrome (check the screenshot above).