[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/components/page_info/page_info_delegate.h b/components/page_info/page_info_delegate.h
index 77810ec8..2b72b54 100644
--- a/components/page_info/page_info_delegate.h
+++ b/components/page_info/page_info_delegate.h
@@ -5,6 +5,8 @@
 #ifndef COMPONENTS_PAGE_INFO_PAGE_INFO_DELEGATE_H_
 #define COMPONENTS_PAGE_INFO_PAGE_INFO_DELEGATE_H_
 
+#include <string>
+
 #include "base/strings/string16.h"
 #include "build/build_config.h"
 #include "components/content_settings/browser/page_specific_content_settings.h"