Add a way to send the resource percentage signal to the RC.

chrome/browser/android/offline_pages/prerendering_loader.cc

Index: chrome/browser/android/offline_pages/prerendering_loader.cc
diff --git a/chrome/browser/android/offline_pages/prerendering_loader.cc b/chrome/browser/android/offline_pages/prerendering_loader.cc
index 5eccbf9f696600b8045c7cfbf5e1cf3c315d6fe7..1e1e7578f41d797af1b584564a0197ee10af5684 100644
--- a/chrome/browser/android/offline_pages/prerendering_loader.cc
+++ b/chrome/browser/android/offline_pages/prerendering_loader.cc
@@ -199,6 +199,21 @@ bool PrerenderingLoader::IsLowbarMet() {
   return is_lowbar_met_;
 }
 
+void PrerenderingLoader::ObserveResourceTracking(
+    const Offliner::ResourceDataType type,
+    int64_t started_count,
+    int64_t completed_count) {
+  // Add the signal to extra data, and use for tracking.
+  if (type == Offliner::ResourceDataType::IMAGE) {
+    double percentage = 100 * static_cast<double>(completed_count) /
+                        static_cast<double>(started_count);
+    // TODO(petewil): Use actual signal type instead of hardcoding name.
+    signal_data_.SetDouble("ImagePercentage", percentage);
+    signal_data_.SetDouble("StartedImages", started_count);
+    signal_data_.SetDouble("CompletedImages", completed_count);
+  }
+}
+
 void PrerenderingLoader::HandleLoadEvent() {
   // If still loading, check if the load succeeded or not, then update
   // the internal state (LOADED for success or IDLE for failure) and post