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This CL adds the groundwork for a slide-in pane to be used by the OOP PDF Viewer. It adheres to the principles of Material Design, and will be used as a base for the bookmarks pane (which will display a list of bookmarks) as well as an info pane to show metadata of the PDF.

BUG=110020

Review URL: https://codereview.chromium.org/864753002

Cr-Commit-Position: refs/heads/master@{#313631}