Log WEBUI_UNTRUSTED_CONTEXT extension functions

Log WEBUI_UNTRUSTED_CONTEXT extension functions such as the
terminalPrivate API used by chrome-untrusted://terminal with new UMA
Extensions.Functions.WebUIUntrustedCalls.

TBR=mlippautz@chromium.org

Bug: 1161001
Change-Id: I188a364c129605205662ab780ab273a894f268ee
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2599649
Commit-Queue: Joel Hockey <joelhockey@chromium.org>
Reviewed-by: Giovanni Ortuño Urquidi <ortuno@chromium.org>
Reviewed-by: Devlin <rdevlin.cronin@chromium.org>
Auto-Submit: Joel Hockey <joelhockey@chromium.org>
Cr-Commit-Position: refs/heads/master@{#839712}

extensions/browser/extension_function_dispatcher.cc

@@ -338,6 +338,10 @@ void ExtensionFunctionDispatcher::DispatchWithCallbackInternal(
     if (function->source_context_type() == Feature::WEBUI_CONTEXT) {
       base::UmaHistogramSparse("Extensions.Functions.WebUICalls",
                                function->histogram_value());
+    } else if (function->source_context_type() ==
+               Feature::WEBUI_UNTRUSTED_CONTEXT) {
+      base::UmaHistogramSparse("Extensions.Functions.WebUIUntrustedCalls",
+                               function->histogram_value());
     }
 
     // Skip the quota, event page, activity logging stuff if there

tools/metrics/histograms/histograms_xml/extensions/histograms.xml

@@ -1751,7 +1751,8 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
   <owner>extensions-core@chromium.org</owner>
   <summary>
     Recorded when a component extension calls an extension API. Recorded once
-    per function call. See also Extensions.Functions.WebUICalls and
+    per function call. See also Extensions.Functions.WebUICalls,
+    Extensions.Functions.WebUIUntrustedCalls, and
     Extensions.Functions.ExtensionCalls.
   </summary>
 </histogram>
@@ -1764,7 +1765,8 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
   <owner>extensions-core@chromium.org</owner>
   <summary>
     Recorded when a non-component extension calls an extension API. Recorded
-    once per function call. See also Extensions.Functions.WebUICalls and
+    once per function call. See also Extensions.Functions.WebUICalls,
+    Extensions.Functions.WebUIUntrustedCalls, and
     Extensions.Functions.ComponentExtensionCalls.
   </summary>
 </histogram>
@@ -1878,7 +1880,22 @@ reviews. Googlers can read more about this at go/gwsq-gerrit.
   <owner>extensions-core@chromium.org</owner>
   <summary>
     Recorded when a WebUI context calls an extension API. Recorded once per
-    function call. See also Extensions.Functions.ComponentExtensionCalls and
+    function call. See also Extensions.Functions.WebUIUntrustedCalls,
+    Extensions.Functions.ComponentExtensionCalls and
+    Extensions.Functions.ExtensionCalls.
+  </summary>
+</histogram>
+
+<histogram name="Extensions.Functions.WebUIUntrustedCalls"
+    enum="ExtensionFunctions" expires_after="never">
+<!-- expires-never: Used for monitoring extension API usage. -->
+
+  <owner>rdevlin.cronin@chromium.org</owner>
+  <owner>extensions-core@chromium.org</owner>
+  <summary>
+    Recorded when a WebUI context calls an extension API. Recorded once per
+    function call. See also Extensions.Functions.WebUICalls,
+    Extensions.Functions.ComponentExtensionCalls and
     Extensions.Functions.ExtensionCalls.
   </summary>
 </histogram>