Clarify browser-side use counter logging for //content code

The existing code only works for code that can depend on
components/page_load_metrics, which excludes all //content code.

This code sample should work everywhere even within //content.

Change-Id: Icb8c2df25097174d50f95163333b13784e8cd1e4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4335937
Reviewed-by: Nan Lin <linnan@chromium.org>
Commit-Queue: Charlie Harrison <csharrison@chromium.org>
Reviewed-by: Yoav Weiss <yoavweiss@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1116951}

docs/use_counter_wiki.md

@@ -25,8 +25,7 @@ feature to UseCounter, simply:
 + Usage can be measured via:
     * MeasureAs=\<enum value\> in the feature's IDL definition; Or
     * blink::UseCounter::Count() for blink side features; Or
-    * page_load_metrics::MetricsWebContentsObserver::RecordFeatureUsage()
-      for browser side features.
+    * content::ContentBrowserClient::LogWebFeatureForCurrentPage() for browser side features.
 
 Example:
 ```c++
@@ -55,7 +54,7 @@ OR
 ```c++
   MyBrowserSideFunction() {
     ...
-    page_load_metrics::MetricsWebContentsObserver::RecordFeatureUsage(
+    GetContentClient()->browser()->LogWebFeatureForCurrentPage(
       render_frame_host, blink::mojom::WebFeature::kMyFeature);
     ...
   }