GitLab

This change adds the header and the Order Summary section to the
Payment Sheet in the Payment Request dialog. Both sheets still need
many tweaks and extra features but this is the first step towards the
dialog actually looking like the design specs.

Mocks here:

https://folio.googleplex.com/chrome-ux/mocks/329-future-web-pay/latest/desktop#

A screenshot of the Payment Sheet is here:

https://drive.google.com/file/d/0B-DVbqI3huZGREpIaE5yMDZjZzA/view?usp=sharing

A screenshot of the Order Summary shown when clicking the Order Summary
row is here:

https://drive.google.com/file/d/0B-DVbqI3huZGM0F0cC1sS2xLTWs/view?usp=sharing

BUG=676112

Review-Url: https://codereview.chromium.org/2592833002
Cr-Commit-Position: refs/heads/master@{#441939}