Provide keyboard shortcut for Distill Page feature

[bsclifton]

Description

We currently offer a Distill Page feature (found under hamburger menu). This condenses the page content and removes the images. While we do offer this, there is no keyboard shortcut for this

If we implement the Speed Reader feature, we'd want to make sure there is a keyboard shortcut also

[bsclifton]

@simonhong would you be able to help me with this one?

[simonhong]

We can add our new accelerator via chrome/browser/ui/views/accelerator_table.cc.
Our shortcut for open tor window is already there.

[bsclifton]

Added speedreader label as I believe we want to make that user facing (and perhaps hide distill)
cc: @rebron