[ios clean] Toolbar accessibility and showcase egtests

ios/chrome/app/strings/ios_strings.grd

Index: ios/chrome/app/strings/ios_strings.grd
diff --git a/ios/chrome/app/strings/ios_strings.grd b/ios/chrome/app/strings/ios_strings.grd
index b1f5fb20677f9cbfa7fdd41c30ab05cc343d4d4b..722471555e2210b1566562c786015bee780ed604 100644
--- a/ios/chrome/app/strings/ios_strings.grd
+++ b/ios/chrome/app/strings/ios_strings.grd
@@ -1426,6 +1426,9 @@ Your data was encrypted with your sync passphrase on <ph name="TIME">$2<ex>Sept
       <message name="IDS_IOS_TOOLBAR_SHOW_TABS" desc="The accessibility label for the toolbar show tabs button [iOS only].">
         Show Tabs
       </message>
+      <message name="IDS_IOS_TOOLBAR_SHOW_TAB_GRID" desc="The accessibility label for the toolbar show tab grid button [iOS only].">
+        Home

[sczs, 2017/06/20 01:20:30]

Wasn't sure on this one, but I know Tab Grid might not have any meaning for
users. 

[marq (ping after 24h), 2017/06/20 08:13:39]

How is this different from IDS_IOS_TOOLBAR_SHOW_TABS's "show tabs"?

[lpromero, 2017/06/20 08:38:53]

I am not sure of that. The spatial layout is accessible to VoiceOver users when
they drag the finger around the screen. Moreover, Switch Control users can see
but don't interact with the screen.
Adding a concept of "Home" here could well be detrimental for when we introduce
Chrome Home (even though we might not officially name it).

[sczs, 2017/06/21 01:47:56]

I was thinking that Tabs is something most people know about (We don't hace Show
Tab Strip), but the concept of Tab Grid hasn't been introduced yet. 

[sczs, 2017/06/21 01:47:56]

I was actually thinking about that, since that button would take you to Chrome
Home. I wasn't thinking of Switch Control users, thanks for bringing that up.
Will change this to Show Tab Grid, Home doesn't make as much sense as I thought.

+      </message>
       <message name="IDS_IOS_TOOLS_MENU" desc="The accessibility label for the iOS tools menu [iOS only]">
         Tools Menu
       </message>