Add settings UI to the memory_inspector

This CL adds the HTML UI for loading/storing backend and
device-specific settings (plus the required server-side wiring).

BUG=340294
NOTRY=true

Review URL: https://codereview.chromium.org/194983005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@256835 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 256835
Add mmap table and resident page UI to memory_inspector.

This wires-up the raw mmap dump (through memdump), introducing:
 - A new /ajax/dump/mmap endpoint to the server.
 - The HTML/JS ui to show the mmap table and the resident page list.


BUG=340294
NOTRY=true

Review URL: https://codereview.chromium.org/196973008

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@256836 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 256836