Child users: add tool-tip string for blocked extensions mature content

For child users, mature extensions should be force-disabled with a
tool-tip explanation. Commit the required string for the tool-tip
before feature freeze on January 17, 2020, so that the translation
team has adequate time to translate the string.

Bug: 1040614
Change-Id: Ide909d6e4f02ff201e2aa5cfd13d11dde1de2df4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2006112
Commit-Queue: Toby Huang <tobyhuang@chromium.org>
Commit-Queue: Ken Rockot <rockot@google.com>
Auto-Submit: Toby Huang <tobyhuang@chromium.org>
Reviewed-by: Ken Rockot <rockot@google.com>
Cr-Commit-Position: refs/heads/master@{#732677}

chrome/app/extensions_strings.grdp

@@ -16,6 +16,9 @@
   <message name="IDS_EXTENSIONS_BACKGROUND_PAGE" desc="Display name for an autogenerated background page.">
     background page
   </message>
+  <message name="IDS_EXTENSIONS_DISABLED_BLOCKED_MATURE" desc="The tooltip displayed when the extension is blocked due to mature content for child users.">
+    This is blocked due to mature content.
+  </message>
   <message name="IDS_EXTENSIONS_CORRUPTED_EXTENSION" desc="The warning for the user that an extension may have been tampered with on disk.">
     This extension may have been corrupted.
   </message>

chrome/app/extensions_strings_grdp/IDS_EXTENSIONS_DISABLED_BLOCKED_MATURE.png.sha1

+6c9f917fe0ca52c374a80b9d663376801a45cb9b
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