Add Android utility CallAfterEnsureMethodsCached

This utility function is used internally to ensure the callback
is triggered when all necessary Java classes and methods are cached.

Author: chkuang-g

app/src/app_android.cc

@@ -573,6 +573,14 @@ bool App::IsDataCollectionDefaultEnabled() const {
 
 const char* App::GetUserAgent() { return app_common::GetUserAgent(); }
 
+void util::CallAfterEnsureMethodsCached(JNIEnv* env, jobject activity,
+                                        std::function<void()> callback) {
+  if (CacheMethods(env, activity)) {
+    callback();
+    ReleaseClasses(env);
+  }
+}
+
 JavaVM* App::java_vm() const { return internal_->java_vm(); }
 
 jobject App::GetPlatformApp() const { return internal_->GetLocalRef(); }

app/src/util_android.h

@@ -1127,6 +1127,12 @@ jint AttachCurrentThread(JavaVM* java_vm, JNIEnv** env);
 // App. If there is no instantiated App, returns nullptr.
 JNIEnv* GetJNIEnvFromApp();
 
+// Make sure the Java classes and methods are cached before triggering the
+// the callback. Can be slow if this is called BEFORE any Firebase App is
+// created.
+void CallAfterEnsureMethodsCached(JNIEnv* env, jobject activity,
+                                  std::function<void()> callback);
+
 }  // namespace util
 // NOLINTNEXTLINE - allow namespace overridden
 }  // namespace firebase