renamed slightly the flag name to be clearer that "Enabled" means "show new navigation"

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/f1beaa8ba96b7bd0bedafb4950945cb974af5b77

commit f1beaa8ba96b7bd0bedafb4950945cb974af5b77
Author: Luciano Pacheco <lucmult@chromium.org>
Date: Wed May 30 04:48:51 2018

Add flag --new-files-app-navigation

This flag will be used to turn on/off the new navigation UI.

Bug:  846585 
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: I983abf571918d899cd5e9938796bf432521e2f07
Reviewed-on: https://chromium-review.googlesource.com/1075924
Reviewed-by: Sasha Morrissey <sashab@chromium.org>
Commit-Queue: Luciano Pacheco <lucmult@chromium.org>
Cr-Commit-Position: refs/heads/master@{#562738}
[modify] https://crrev.com/f1beaa8ba96b7bd0bedafb4950945cb974af5b77/chrome/browser/about_flags.cc
[modify] https://crrev.com/f1beaa8ba96b7bd0bedafb4950945cb974af5b77/chrome/browser/flag_descriptions.cc
[modify] https://crrev.com/f1beaa8ba96b7bd0bedafb4950945cb974af5b77/chrome/browser/flag_descriptions.h
[modify] https://crrev.com/f1beaa8ba96b7bd0bedafb4950945cb974af5b77/chromeos/chromeos_switches.cc
[modify] https://crrev.com/f1beaa8ba96b7bd0bedafb4950945cb974af5b77/chromeos/chromeos_switches.h
[modify] https://crrev.com/f1beaa8ba96b7bd0bedafb4950945cb974af5b77/tools/metrics/histograms/enums.xml
[modify] https://crrev.com/f1beaa8ba96b7bd0bedafb4950945cb974af5b77/ui/file_manager/file_manager/common/js/util.js

The flag has landed, but the feature behind the flag is still being developed.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/a0e2753f75c926313e183b912584a7f15790825d

commit a0e2753f75c926313e183b912584a7f15790825d
Author: Luciano Pacheco <lucmult@chromium.org>
Date: Mon Jul 16 07:41:10 2018

Rename the "My Files" flag to disable-my-files-navigation

"My Files" is on by default after crrev.com/c/1131025. Rename
the "My Files" flag to disable-my-files-navigation so can turn
it off.

Bug:  846587 ,  846585 
Cq-Include-Trybots: luci.chromium.try:closure_compilation
Change-Id: I987230566c383fd8385f65916704cd0e9b32fd27
Reviewed-on: https://chromium-review.googlesource.com/1136456
Reviewed-by: Noel Gordon <noel@chromium.org>
Commit-Queue: Noel Gordon <noel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#575203}
[modify] https://crrev.com/a0e2753f75c926313e183b912584a7f15790825d/chrome/browser/about_flags.cc
[modify] https://crrev.com/a0e2753f75c926313e183b912584a7f15790825d/chrome/browser/flag_descriptions.cc
[modify] https://crrev.com/a0e2753f75c926313e183b912584a7f15790825d/chrome/browser/flag_descriptions.h
[modify] https://crrev.com/a0e2753f75c926313e183b912584a7f15790825d/chromeos/chromeos_switches.cc
[modify] https://crrev.com/a0e2753f75c926313e183b912584a7f15790825d/chromeos/chromeos_switches.h
[modify] https://crrev.com/a0e2753f75c926313e183b912584a7f15790825d/tools/metrics/histograms/enums.xml
[modify] https://crrev.com/a0e2753f75c926313e183b912584a7f15790825d/ui/file_manager/file_manager/common/js/util.js
[modify] https://crrev.com/a0e2753f75c926313e183b912584a7f15790825d/ui/file_manager/file_manager/foreground/js/file_manager.js
[modify] https://crrev.com/a0e2753f75c926313e183b912584a7f15790825d/ui/file_manager/file_manager/foreground/js/navigation_list_model.js