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Update PlatformStyle to return different borders for Material Design
LabelButtons. Removing asset borders on Chrome OS, and hover effects on Windows
and Linux.

Updated ToolbarButton to remove its local implementation of this behaviour.

Updated WrenchToolbarButton to use a image asset for Material Design, and to not
initialize WrenchIconPainter.

TEST=manual testing on device
BUG=505801, 495654

Review URL: https://codereview.chromium.org/1270343004

Cr-Commit-Position: refs/heads/master@{#342414}