Good work! I'm excited to see other pages extend their own custom keyboard shortcuts from this in the future. Just some small things that could help with wording

Could change the wording from The dictionary to A dictionary

use shortcut instead of shortcuts

Try This key selects the previous comment. instead

Try This key selects the next file. instead

Try This key selects the previous diff. instead

Try This key selects the next diff. instead

Try This key selects the previous comment. instead

Try This key selects the next comment. instead

I'm not totally sure what this commands does on my first read through. I think changing the wording for this will help clear up confusion with users

Try This key creates a new comment. instead

Could remove this console.log statement

just to clarify how the keyboard shortcuts work, would pressing any key in for example 'aAKP<m' trigger the shortcut? 
also i think it would be helpful to link to any mockups or additional work related to this review request because it's not super clear from this work alone what you're trying to accomplish.

i think we usually use extend as opposed to expand

not sure but i think defining keyBindings like this will overwrite the parent object; it's not a problem atm since the parent object is empty, but if we end up having global key bindings they won't work on these pages because they'll be overwritten. i think you want something like this:
keyBindings: _.extend({
    ...
    }, RB.PageView.prototype.keyBindings),

i would prefer doc instead of help since it feels more specific but this is up to interpretation

Hi Xiaohui,
This looks like a great approach to me! Just a few minor suggestions.

Nit: "help texts" -> "help text"
We should also indicate what fields are expected in the dictionary. What is the key supposed to be? What can the values be?

I wonder if we should be more explicit in encouraging subclasses to extend this, by saying "Subclasses should extend this instead of replacing it".

"&" -> "and"

It would be great if this could document each key that's expected by an entry, using a format similar to our "Args".

"consisting"

For each of these, can you wrap the string with gettext()? That'll prepare it for localization.

We should also leave off the "This key" part. Just like:

"Select the previous file."
"Select the next diff."
"Re-center the selected diff chunk."
"Create a comment."

etc.