Memory screen: implement profile diff.

[polina-c]

go/devtools-memory-page-vision

Build:

• [x] crud for snapshots
• [x] fakes for memory page
• [x] show snapshot stats
• [x] show diff stats
• [x] show diff details
• [x] export to CSV
• [ ] search by class / library
• [ ] heap taking and comparison asynchronous
• [ ] Support button 'Clear' and 'Export' on the control pane

Clean up:

• [ ] experiment with Gallery
• [ ] test cover
• [ ] documentation
• [ ] release notes
• [ ] UX research - go/devtools-memory-diff-ux-research

[polina-c]

Diff snapshot in Chrome devtools:

See https://www.youtube.com/watch?v=63Os4MbobNM

[terrylucas]

Got it.