MD Settings: validate home button url input

chrome/app/settings_strings.grdp

Index: chrome/app/settings_strings.grdp
diff --git a/chrome/app/settings_strings.grdp b/chrome/app/settings_strings.grdp
index 61993ae8a1f6f0475b0dd8445561d1dbf2833c7c..5acbc6c9aea86679c34e1fbdc139296fdecf7e7b 100644
--- a/chrome/app/settings_strings.grdp
+++ b/chrome/app/settings_strings.grdp
@@ -240,6 +240,9 @@
   <message name="IDS_SETTINGS_HOME_BUTTON_DISABLED" desc="Sub label for the Show home button setting when disabled.">
     Disabled
   </message>
+  <message name="IDS_SETTINGS_HOME_URL_NOT_VALID" desc="Text indicating that the input to the custom home url is not invalid.">
+   Not valid

[dpapad, 2017/03/24 01:39:31]

Can we reuse/repurpose the existing identical message at
https://cs.chromium.org/chromium/src/chrome/app/settings_strings.grdp?l=1732-...

[scottchen, 2017/03/24 20:48:54]

I feel like there's always a good chance strings used in different sections
could change, so I made a new one for easier maintainability. Do we save much by
reusing the same string?

[dpapad, 2017/03/24 21:47:43]

I think is better to be frugal with our strings and only fork a string once (if
ever) the need arises, instead of preemptively having them as separate, just in
case.

We have a large set of shared strings, meaning that they are used in multiple UI
surfaces in Settings, see
https://cs.chromium.org/chromium/src/chrome/browser/ui/webui/settings/md_sett....
Every string gets translated in 40+ languages that Chrome supports. This
generates additional work for the translation team, and also means that the 40+
translated copies of the identical string are included in the final binary
(AFAIK the translations are not downloaded on-demand).

[scottchen, 2017/03/24 22:56:30]

Acknowledged.

+  </message>
   <message name="IDS_SETTINGS_SET_WALLPAPER" desc="Name of the control which allows the user to set the wallpaper.">
     Wallpaper
   </message>