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This CL moves magic numbers to constants files:

- Various dimensions in GridCell
- Margins and height of TabGridTopToolbar
- Margins and height of TabGridBottomToolbar

This CL also changes the toolbar classes to use
|-willMoveToSuperview:| to setup views instead of
|-init|.

Bug: 818198, 822524

Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet;master.tryserver.chromium.mac:ios-simulator-full-configs
Change-Id: Ib4dcfd344c29c3e0ccee103b6002dd6e1d14fb30
Reviewed-on: https://chromium-review.googlesource.com/965576
Commit-Queue: edchin <edchin@chromium.org>
Reviewed-by: edchin <edchin@chromium.org>
Reviewed-by: Mark Cogan <marq@chromium.org>
Cr-Commit-Position: refs/heads/master@{#543790}