General comment cleaning / refactoring for Mac Installer

chrome/installer/mac/app/OmahaXMLParser.m

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #import "OmahaXMLParser.h"
 
 @interface OmahaXMLParser ()<NSXMLParserDelegate>
 @end
 
 @implementation OmahaXMLParser {
@@ skipping 14 matching lines @@
   }
 
   NSMutableArray* completeDownloadURLs = [[NSMutableArray alloc] init];
   for (NSString* URL in omahaParser->chromeIncompleteDownloadURLs_) {
     [completeDownloadURLs
         addObject:[NSURL URLWithString:omahaParser->chromeImageFilename_
                          relativeToURL:[NSURL URLWithString:URL]]];
   }
 
   if ([completeDownloadURLs count] < 1) {
-    // TODO: currently whatever error is passed in doesn't matter... we should
-    // make it so that the type of error informs what the installer will do
-    // about the error
+    // TODO: The below error exists only so the caller of this method would
+    // catch the error created here. A better way to handle this is to make the
+    // error's contents inform what the installer will try next when it attempts
+    // to recover from an issue.
     *error = [NSError errorWithDomain:@"ChromeErrorDomain" code:1 userInfo:nil];
     return nil;
   }
 
   return completeDownloadURLs;
 }
 
-// Method implementation for XMLParserDelegate.
 // Searches the XML data for the tag "URL" and the subsequent "codebase"
 // attribute that indicates a URL follows. Copies each URL into an array.
-// Note that the URLs in the XML file are incomplete. They need the filename
+// NOTE: The URLs in the XML file are incomplete. They need the filename
 // appended to end. The second if statement checks for the tag "package" which
 // contains the filename needed to complete the URLs.
 - (void)parser:(NSXMLParser*)parser
     didStartElement:(NSString*)elementName
        namespaceURI:(NSString*)namespaceURI
       qualifiedName:(NSString*)qName
          attributes:(NSDictionary*)attributeDict {
   if ([elementName isEqualToString:@"url"]) {
     if (!chromeIncompleteDownloadURLs_) {
       chromeIncompleteDownloadURLs_ = [[NSMutableArray alloc] init];
@@ skipping 10 matching lines @@
 // If either component of the URL is empty then the complete URL cannot
 // be generated so both variables are set to nil to flag errors.
 - (void)parserDidEndDocument:(NSXMLParser*)parser {
   if (!chromeIncompleteDownloadURLs_ || !chromeImageFilename_) {
     chromeIncompleteDownloadURLs_ = nil;
     chromeImageFilename_ = nil;
   }
 }
 
 @end