Add telemetry collector and methods to RumInjector

Author: sarahchen6

internal-api/src/main/java/datadog/trace/api/rum/RumInjector.java

@@ -27,6 +27,9 @@ public final class RumInjector {
   private final DDCache<String, byte[]> markerCache;
   private final Function<String, byte[]> snippetBytes;
 
+  // Health metrics telemetry collector (set by CoreTracer)
+  private static volatile RumTelemetryCollector telemetryCollector = RumTelemetryCollector.NO_OP;
+
   RumInjector(Config config) {
     boolean rumEnabled = config.isRumEnabled();
     RumInjectorConfig injectorConfig = config.getRumInjectorConfig();
@@ -120,4 +123,23 @@ public byte[] getMarkerBytes(String encoding) {
     }
     return this.markerCache.computeIfAbsent(encoding, MARKER_BYTES);
   }
+
+  public static void setTelemetryCollector(RumTelemetryCollector collector) {
+    telemetryCollector = collector != null ? collector : RumTelemetryCollector.NO_OP;
+  }
+
+  // report that the RUM injector succeeded in injecting the SDK in an HTTP response
+  public static void reportInjectionSucceed() {
+    telemetryCollector.onInjectionSucceed();
+  }
+
+  // report that the RUM injector failed to inject the SDK in an HTTP response
+  public static void reportInjectionFailed() {
+    telemetryCollector.onInjectionFailed();
+  }
+
+  // report that the RUM injector skipped injecting the SDK in an HTTP response
+  public static void reportInjectionSkipped() {
+    telemetryCollector.onInjectionSkipped();
+  }
 }

internal-api/src/main/java/datadog/trace/api/rum/RumTelemetryCollector.java

@@ -0,0 +1,26 @@
+package datadog.trace.api.rum;
+
+// Collect RUM injection telemetry
+public interface RumTelemetryCollector {
+
+  RumTelemetryCollector NO_OP =
+      new RumTelemetryCollector() {
+        @Override
+        public void onInjectionSucceed() {}
+
+        @Override
+        public void onInjectionFailed() {}
+
+        @Override
+        public void onInjectionSkipped() {}
+      };
+
+  // call when RUM injection succeeds
+  void onInjectionSucceed();
+
+  // call when RUM injection fails
+  void onInjectionFailed();
+
+  // call when RUM injection is skipped
+  void onInjectionSkipped();
+}