Add the ability to trace methods in internal builds.

Currently only for internal builds. Use the @Trace annotation to trace
methods for viewing in Perfetto.

app/src/website/java/org/thoughtcrime/securesms/tracing/TracerImpl.java

@@ -0,0 +1,34 @@
+package org.thoughtcrime.securesms.tracing;
+
+import androidx.annotation.NonNull;
+
+/**
+ * Dummy implementation.
+ */
+final class TracerImpl implements Tracer {
+
+  @Override
+  public boolean isEnabled() {
+    return false;
+  }
+
+  @Override
+  public void start(@NonNull String methodName) {
+    throw new UnsupportedOperationException();
+  }
+
+  @Override
+  public void start(@NonNull String methodName, @NonNull String key, @NonNull String value) {
+    throw new UnsupportedOperationException();
+  }
+
+  @Override
+  public void end(@NonNull String methodName) {
+    throw new UnsupportedOperationException();
+  }
+
+  @Override
+  public @NonNull byte[] serialize() {
+    throw new UnsupportedOperationException();
+  }
+}