[Telemetry] Move page quiescence test to WebContents

tools/telemetry/telemetry/core/network_quiescence.js

Index: tools/telemetry/telemetry/core/network_quiescence.js
diff --git a/tools/perf/metrics/speedindex.js b/tools/telemetry/telemetry/core/network_quiescence.js
similarity index 60%
rename from tools/perf/metrics/speedindex.js
rename to tools/telemetry/telemetry/core/network_quiescence.js
index c64f38b1667be1901935f3ec6afb6b9cc3a8f2a5..d49db5b1ff1d3749a736e75aa093c999f1e6ab2b 100644
--- a/tools/perf/metrics/speedindex.js
+++ b/tools/telemetry/telemetry/core/network_quiescence.js
@@ -6,10 +6,16 @@
 
 /**
  * @fileoverview This file provides a JavaScript helper function that
- * determines when the last resource was received.
+ * determines when network quiescence has been reached based on the time since
+ * the last resource was received.
  */
 (function() {
 
+  // Make executing this code idempotent.
+  if (window.__telemetry_testHasReachedNetworkQuiescence) {
+    return;
+  }
+
   // Set the Resource Timing interface functions that will be used below
   // to use whatever version is available currently regardless of vendor
   // prefix.
@@ -38,19 +44,32 @@
   // so we can clear new entries when they're added.
   var lastEntry = null;
 
+  // True when no resource has been loaded from the network for
+  //|QUIESCENCE_TIMEOUT_MS| milliseconds. This value is sticky.
+  var hasReachedQuiesence = false;
+
+  // Time to wait before declaring network quiescence in milliseconds.
+  var QUIESCENCE_TIMEOUT_MS = 2000;
+
   /**
    * This method uses the Resource Timing interface, which is described at
-   * http://www.w3.org/TR/resource-timing/. It provides information about
-   * timings for resources such as images and script files, and it includes
-   * resources requested via XMLHttpRequest.
+   * http://www.w3.org/TR/resource-timing/. It determines whether the time
+   * since lodading any resources such as images and script files (including
+   * resources requested via XMLHttpRequest) has exceeded a threshold defined
+   # by |QUIESCENCE_TIMEOUT_MS|.
    *
-   * @return {number} The time since either the load event, or the last
-   *   the last resource was received after the load event. If the load
-   *   event hasn't yet happened, return 0.
+   * @return {boolean} True if the time since either the load event, or the last
+   *   resource was received after the load event exceeds the aforementioned
+   *   threshold. This state is sticky, so once this function returns true for a
+   *   given page, it will always return true.
    */
-  window.timeSinceLastResponseAfterLoadMs = function() {
+  window.__telemetry_testHasReachedNetworkQuiescence = function() {
+    if (hasReachedQuiesence) {
+      return true;
+    }
+
     if (window.document.readyState !== 'complete') {
-      return 0;
+      return false;
     }
 
     var resourceTimings = window.performance.getEntriesByType('resource');
@@ -64,13 +83,21 @@
     // so we must also get load time in the same terms.
     var timing = window.performance.timing;
     var loadTime = timing.loadEventEnd - timing.navigationStart;
+    var lastResponseTimeMs = 0;
 
     // If there have been no resource timing entries, or the last entry was
-    // before the load event, then return the time since the load event.
+    // before the load event, then use the time since the load event.
     if (!lastEntry || lastEntry.responseEnd < loadTime) {
-      return window.performance.now() - loadTime;
+      lastResponseTimeMs = window.performance.now() - loadTime;
+    } else {
+      lastResponseTimeMs = window.performance.now() - lastEntry.responseEnd;
+    }
+
+    if (lastResponseTimeMs >= QUIESCENCE_TIMEOUT_MS) {
+      hasReachedQuiesence = true;
     }
-    return window.performance.now() - lastEntry.responseEnd;
+
+    return hasReachedQuiesence;
   }
 
 })();