Bug 1465424 - Added 3 histograms to test font editor usage assumptions; r=rcaliman

MozReview-Commit-ID: BIkqEzp5BNA

--HG--
extra : rebase_source : 376ba65ab069bd35b29672a29c8ee723af9bad90

devtools/client/inspector/fonts/fonts.js

@@ -55,6 +55,10 @@ const REGISTERED_AXES_TO_FONT_PROPERTIES = {
 };
 const REGISTERED_AXES = Object.keys(REGISTERED_AXES_TO_FONT_PROPERTIES);
 
+const HISTOGRAM_N_FONT_AXES = "DEVTOOLS_FONTEDITOR_N_FONT_AXES";
+const HISTOGRAM_N_FONTS_RENDERED = "DEVTOOLS_FONTEDITOR_N_FONTS_RENDERED";
+const HISTOGRAM_FONT_TYPE_DISPLAYED = "DEVTOOLS_FONTEDITOR_FONT_TYPE_DISPLAYED";
+
 class FontInspector {
   constructor(inspector, window) {
     this.cssProperties = getCssProperties(inspector.toolbox);
@@ -601,6 +605,34 @@ class FontInspector {
            !this.inspector.selection.isPseudoElementNode();
   }
 
+  /**
+   * Upon a new node selection, log some interesting telemetry probes.
+   */
+  logTelemetryProbesOnNewNode() {
+    const { fontData, fontEditor } = this.store.getState();
+    const { telemetry } = this.inspector;
+
+    // Log the number of font faces used to render content of the element.
+    const nbOfFontsRendered = fontData.fonts.length;
+    if (nbOfFontsRendered) {
+      telemetry.getHistogramById(HISTOGRAM_N_FONTS_RENDERED).add(nbOfFontsRendered);
+    }
+
+    // Log data about the currently edited font (if any).
+    // Note that the edited font is always the first one from the fontEditor.fonts array.
+    const editedFont = fontEditor.fonts[0];
+    if (!editedFont) {
+      return;
+    }
+
+    const nbOfAxes = editedFont.variationAxes ? editedFont.variationAxes.length : 0;
+    telemetry.getHistogramById(HISTOGRAM_FONT_TYPE_DISPLAYED).add(
+      !nbOfAxes ? "nonvariable" : "variable");
+    if (nbOfAxes) {
+      telemetry.getHistogramById(HISTOGRAM_N_FONT_AXES).add(nbOfAxes);
+    }
+  }
+
   /**
    * Sync the Rule view with the latest styles from the page. Called in a debounced way
    * (see constructor) after property changes are applied directly to the CSS style rule
@@ -686,8 +718,9 @@ class FontInspector {
   onNewNode() {
     this.ruleView.off("property-value-updated", this.onRulePropertyUpdated);
     if (this.isPanelVisible()) {
-      this.update();
-      this.refreshFontEditor();
+      Promise.all([this.update(), this.refreshFontEditor()]).then(() => {
+        this.logTelemetryProbesOnNewNode();
+      }).catch(e => console.error(e));
     }
   }
 

toolkit/components/telemetry/Histograms.json

@@ -10155,6 +10155,38 @@
     "description": "On page load, record the number of CSS Grid elements present on a page when the DevTools is open",
     "releaseChannelCollection": "opt-out"
   },
+  "DEVTOOLS_FONTEDITOR_N_FONT_AXES": {
+    "record_in_processes": ["main"],
+    "alert_emails": ["dev-developer-tools@lists.mozilla.org", "mbalfanz@mozilla.com"],
+    "expires_in_version": "66",
+    "bug_numbers": [1465424],
+    "description": "Indicates the number of variation axes of the variable fonts that are displayed in the font editor UI",
+    "releaseChannelCollection": "opt-out",
+    "kind": "exponential",
+    "high": 100,
+    "n_buckets": 20
+  },
+  "DEVTOOLS_FONTEDITOR_N_FONTS_RENDERED": {
+    "record_in_processes": ["main"],
+    "alert_emails": ["dev-developer-tools@lists.mozilla.org", "mbalfanz@mozilla.com"],
+    "expires_in_version": "66",
+    "bug_numbers": [1465424],
+    "description": "Indicates how many fonts the font editor displayed as being needed to render the selected element's content",
+    "releaseChannelCollection": "opt-out",
+    "kind": "exponential",
+    "high": 50,
+    "n_buckets": 10
+  },
+  "DEVTOOLS_FONTEDITOR_FONT_TYPE_DISPLAYED": {
+    "record_in_processes": ["main"],
+    "alert_emails": ["dev-developer-tools@lists.mozilla.org", "mbalfanz@mozilla.com"],
+    "expires_in_version": "66",
+    "bug_numbers": [1465424],
+    "description": "Indicates if the font editor displayed its UI for a non-variable font or a variable font",
+    "releaseChannelCollection": "opt-out",
+    "kind": "categorical",
+    "labels": ["variable", "nonvariable"]
+  },
   "BROWSER_IS_USER_DEFAULT": {
     "record_in_processes": ["main"],
     "expires_in_version": "never",