pdf: Implement UX spec for icon states

* Adjusts size/location of icons and focus/hover/active states.
* Makes viewer-toolbar-dropdown use a single paper-button to avoid overlapping focus/ripple.
* Removes focus when a dropdown is cancelled by pointer events.

Spec: go/pdf-icon-states-spec
Impl: go/pdf-icon-states-impl

Bug: 902646
Change-Id: If3bee9f86c8fa9f50537c8ff3cc4e3a9011172eb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1508014
Commit-Queue: dstockwell <dstockwell@chromium.org>
Commit-Queue: dsinclair <dsinclair@chromium.org>
Reviewed-by: dsinclair <dsinclair@chromium.org>
Auto-Submit: dstockwell <dstockwell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#638574}
5 files changed