[LSC] Add #include <string> to prepare for removal of base::string16

This change adds #include <string> to files currently including
"base/strings/string16.h". This prepares these files for the planned
removal of the base::string16 alias.

In order to adhere to the style guide [1] the following logic was
performed:

* Insert into an existing block of C++ STL includes, if possible
* Else insert `#include <string>` followed by a newline before the first
  #include "some_header.h" line that is not referring to a matching header
  (only relevant for implementation and test files)

[1] https://google.github.io/styleguide/cppguide.html#Names_and_Order_of_Includes

Bug: 1184339
Change-Id: I96660fec3fff0192d53e9728bbbae86228a52c58
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2749296
Commit-Queue: Jan Wilken Dörrie <[email protected]>
Owners-Override: Jan Wilken Dörrie <[email protected]>
Reviewed-by: Peter Kasting <[email protected]>
Cr-Commit-Position: refs/heads/master@{#861966}
diff --git a/chrome/browser/ui/webui/help/version_updater_basic.cc b/chrome/browser/ui/webui/help/version_updater_basic.cc
index dd5eae7..a843b38 100644
--- a/chrome/browser/ui/webui/help/version_updater_basic.cc
+++ b/chrome/browser/ui/webui/help/version_updater_basic.cc
@@ -4,6 +4,8 @@
 
 #include "chrome/browser/ui/webui/help/version_updater_basic.h"
 
+#include <string>
+
 #include "base/strings/string16.h"
 #include "chrome/browser/upgrade_detector/upgrade_detector.h"