Backporting documentation changes (firebase#550)

Author: rsgowman

firebase-firestore/src/main/java/com/google/firebase/firestore/FirebaseFirestore.java

@@ -376,21 +376,22 @@ public static void setLoggingEnabled(boolean loggingEnabled) {
  }
 
  /**
- * Clears the persistent storage. This includes pending writes and cached documents.
+ * Clears the persistent storage, including pending writes and cached documents.
  *
- * <p>Must be called while the firestore instance is not started (after the app is shutdown or
- * when the app is first initialized). On startup, this method must be called before other methods
- * (other than setFirestoreSettings()). If the firestore instance is still running, the Task will
- * fail with an error code of FAILED_PRECONDITION.
+ * <p>Must be called while the FirebaseFirestore instance is not started (after the app is
+ * shutdown or when the app is first initialized). On startup, this method must be called before
+ * other methods (other than <code>setFirestoreSettings()</code>). If the FirebaseFirestore
+ * instance is still running, the <code>Task</code> will fail with an error code of
+ * <code>FAILED_PRECONDITION</code>.
  *
- * <p>Note: clearPersistence() is primarily intended to help write reliable tests that use
- * Firestore. It uses the most efficient mechanism possible for dropping existing data but does
+ * <p>Note: <code>clearPersistence()</code> is primarily intended to help write reliable tests
+ * that use Cloud Firestore. It uses an efficient mechanism for dropping existing data but does
  * not attempt to securely overwrite or otherwise make cached data unrecoverable. For applications
- * that are sensitive to the disclosure of cache data in between user sessions we strongly
- * recommend not to enable persistence in the first place.
+ * that are sensitive to the disclosure of cached data in between user sessions, we strongly
+ * recommend not enabling persistence at all.
  *
- * @return A Task that is resolved once the persistent storage has been cleared. Otherwise, the
- * Task is rejected with an error.
+ * @return A <code>Task</code> that is resolved when the persistent storage is cleared. Otherwise,
+ * the <code>Task</code> is rejected with an error.
  */
  @PublicApi
  public Task<Void> clearPersistence() {