Use views::style for buttons, bootstrap ash_typography to do so.

This makes LabelButton::AdjustFontSize() obsolete.

LabelButton::SetFontSize() is also mostly obsolete. Remove it. Two
remaining cases are button subclasses that are never "default" buttons
so they can just set the font list on the button->label() directly.

BUG=691891, 623987
TEST=LabelButtonTest.TextSizeFromContext (replaces AdjustFontSize)

Review-Url: https://codereview.chromium.org/2801583002
Cr-Commit-Position: refs/heads/master@{#472019}

• ash/public/cpp/BUILD.gn[diff]
• ash/public/cpp/ash_typography.cc[Added - diff]
• ash/public/cpp/ash_typography.h[Added - diff]
• ash/system/session/logout_button_tray.cc[diff]
• ash/system/toast/toast_overlay.cc[diff]
• chrome/browser/ui/views/harmony/chrome_typography.cc[diff]
• chrome/browser/ui/views/harmony/chrome_typography.h[diff]
• chrome/browser/ui/views/harmony/harmony_typography_provider.cc[diff]
• chrome/browser/ui/views/harmony/layout_provider_unittest.cc[diff]
• chrome/browser/ui/views/profiles/avatar_button.cc[diff]
• chrome/browser/ui/views/toolbar/app_menu.cc[diff]
• ui/views/controls/button/label_button.cc[diff]
• ui/views/controls/button/label_button.h[diff]
• ui/views/controls/button/label_button_unittest.cc[diff]
• ui/views/controls/button/md_text_button.cc[diff]
• ui/views/controls/button/md_text_button.h[diff]
• ui/views/style/typography.h[diff]
• ui/views/style/typography_provider.cc[diff]
• ui/views/style/typography_provider.h[diff]
• ui/views/touchui/touch_selection_menu_runner_views.cc[diff]