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Adds a new dialog class based on our current UX mocks. The intention
is to iterate with the UX team to come up with a UI for the Chrome
Cleanup tool.

Some functionality is currently missing and will be added in
subsequent CLs:
- Checkbox to ask for logs upload permissions
- Animation when the details section is expanded/folded

BUG=690020

Review-Url: https://codereview.chromium.org/2795133002
Cr-Commit-Position: refs/heads/master@{#462669}