Deprecated Code Report

The patch could apply, but its changes are not correct.

+  \Drupal::database()->schema()->changeField('drupalchat_msg', 'uid1', 'uid1',
     array(
         'description' => 'Uid of the sender.',
         'type' => 'varchar',
         'length' => 32,
         'not null' => TRUE,
     ));

Since that code is changed, the indentation of the array lines must be corrected too.

-  if (!db_index_exists('drupalchat_msg','uid1')) {
-    db_add_index('drupalchat_msg','uid1',array('uid1'));
+  if (!\Drupal::database()->schema()->indexExists('drupalchat_msg','uid1')) {
+    \Drupal::database()->schema()->indexExists('drupalchat_msg','uid1',array('uid1'));
   }

The existing code is adding an index if it does not exist. The changed code is checking twice if the index exist.
Also, per Drupal coding standards, there must be a space after the commas between function/method arguments.

-  if (!db_index_exists('drupalchat_msg','uid2')) {
-    db_add_index('drupalchat_msg','uid2',array('uid2'));
+  if (!\Drupal::database()->schema()->indexExists('drupalchat_msg','uid2')) {
+    \Drupal::database()->schema()->addIndex('drupalchat_msg','uid2',array('uid2'));
   }
-  if (!db_index_exists('drupalchat_users','uid')) {
-    db_add_index('drupalchat_users','uid',array('uid'));
+  if (!\Drupal::database()->schema()->indexExists('drupalchat_users','uid')) {
+    \Drupal::database()->schema()->addIndex('drupalchat_users','uid',array('uid'));
   }
-  if (!db_index_exists('drupalchat_users','session')) {
-    db_add_index('drupalchat_users','session',array('session'));
+  if (!\Drupal::database()->schema()->indexExists('drupalchat_users','session')) {
+    \Drupal::database()->schema()->addIndex('drupalchat_users','session',array('session'));

There are missing spaces after commas.

+  if(!\Drupal::database()->schema()->fieldExists('drupalchat_msg', 'message_id')) {
+    \Drupal::database()->schema()->addField('drupalchat_msg', 'message_id', array(
         'type' => 'varchar',
         'length' => 50,
         'not null' => TRUE,

Since that code is changed, the last lines must be correctly indented too.

-  			$attachments['#attached']['library'][] = 'drupalchat/drupalchat-popup';	
+  			$attachments['#attached']['library'][] = 'drupalchat/drupalchat-popup';
   		}else if($drupalchat_path_visibility == 1 && !(\Drupal::service('router.admin_context')->isAdminRoute())){
-  			$attachments['#attached']['library'][] = 'drupalchat/drupalchat-popup';	
+  			$attachments['#attached']['library'][] = 'drupalchat/drupalchat-popup';

Since the purpose of this issue removing calls to functions that have been removed, those changes are off-topic. If the lines that call deprecated functions are also correctly formatted, that is correct, but it is not correct to re-format all the existing lines, or this issue would become Fix the warnings/errors reported by PHP_CodeSniffer, for which there is already an open issue.

Made changes according to #7.

Please review.