ui: Cleanup class/struct forward declarations

base/android/jni_weak_ref.h

Index: base/android/jni_weak_ref.h
diff --git a/base/android/jni_weak_ref.h b/base/android/jni_weak_ref.h
index 2ae5cce02755c2833a2ab97acd71428a63cec2a5..223c47b2a2a5bd2fd10d392b0e2517a61ebb6267 100644
--- a/base/android/jni_weak_ref.h
+++ b/base/android/jni_weak_ref.h
@@ -29,7 +29,11 @@ class BASE_EXPORT JavaObjectWeakGlobalRef {
 
   base::android::ScopedJavaLocalRef<jobject> get(JNIEnv* env) const;
 
-  bool is_empty() const { return obj_ == nullptr; }
+  // Returns true if the weak reference has not been initialized to point at
+  // an object (or ḣas had reset() called).
+  // Do not call this to test if the object referred to still exists! The weak
+  // reference remains initialized even if the target object has been collected.
+  bool is_uninitialized() const { return obj_ == nullptr; }
 
   void reset();