Bug 1702248 - Limit encoding detection outcome telemetry to top level and to text/html and text/plain. r=emk

Differential Revision: https://phabricator.services.mozilla.com/D110902

parser/html/nsHtml5TreeOpExecutor.cpp

@@ -210,9 +210,24 @@ nsHtml5TreeOpExecutor::DidBuildModel(bool aTerminated) {
   if (mStarted) {
     mDocument->EndLoad();
 
+    // Gather telemetry only for top-level content navigations in order to
+    // avoid noise from ad iframes.
+    bool topLevel = false;
+    if (BrowsingContext* bc = mDocument->GetBrowsingContext()) {
+      topLevel = bc->IsTopContent();
+    }
+
+    // Gather telemetry only for text/html and text/plain (excluding CSS, JS,
+    // etc. being viewed as text.)
+    nsAutoString contentType;
+    mDocument->GetContentType(contentType);
+    bool htmlOrPlain = contentType.EqualsLiteral(u"text/html") ||
+                       contentType.EqualsLiteral(u"text/plain");
+
     // Gather chardetng telemetry
     MOZ_ASSERT(mDocument->IsHTMLDocument());
-    if (!aTerminated && !mDocument->AsHTMLDocument()->IsViewSource()) {
+    if (htmlOrPlain && topLevel && !aTerminated &&
+        !mDocument->AsHTMLDocument()->IsViewSource()) {
       // We deliberately measure only normally-completed (non-aborted) loads
       // that are not View Source loads. This seems like a better place for
       // checking normal completion than anything in nsHtml5StreamParser.

toolkit/components/telemetry/Histograms.json

@@ -8533,7 +8533,7 @@
     "record_in_processes": ["main", "content"],
     "products": ["firefox"],
     "alert_emails": ["hsivonen@mozilla.com"],
-    "bug_numbers": [1686463],
+    "bug_numbers": [1686463, 1702248],
     "expires_in_version": "91",
     "releaseChannelCollection": "opt-out",
     "kind": "categorical",
@@ -8544,7 +8544,7 @@
     "record_in_processes": ["main", "content"],
     "products": ["firefox"],
     "alert_emails": ["hsivonen@mozilla.com"],
-    "bug_numbers": [1686463],
+    "bug_numbers": [1686463, 1702248],
     "expires_in_version": "91",
     "releaseChannelCollection": "opt-out",
     "kind": "categorical",