Add more string_util functions to base namespace.

Moves ReplaceFirstSubstringAfterOffset. It also changes the find/replace arguments to be string pieces (normally these are constants).

TBR=gauravsh@chromium.org for chromeos/network

Review URL: https://codereview.chromium.org/1200393002

Cr-Original-Commit-Position: refs/heads/master@{#335999}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: e6dae46fc681a8ad62f6937a6ac1cab3d51938a9

tools/gn/command_args.cc

diff --git a/tools/gn/command_args.cc b/tools/gn/command_args.cc
index 518a1b6..a8b0097 100644
--- a/tools/gn/command_args.cc
+++ b/tools/gn/command_args.cc
@@ -211,7 +211,7 @@
   // but quoting and escaping internal quotes should handle 99.999% of all
   // cases.
   std::string escaped_name = file_to_edit.value();
-  ReplaceSubstringsAfterOffset(&escaped_name, 0, "\"", "\\\"");
+  base::ReplaceSubstringsAfterOffset(&escaped_name, 0, "\"", "\\\"");
   cmd.append(escaped_name);
   cmd.push_back('"');
 
@@ -250,7 +250,8 @@
 #if defined(OS_WIN)
       // Use Windows lineendings for this file since it will often open in
       // Notepad which can't handle Unix ones.
-      ReplaceSubstringsAfterOffset(&argfile_default_contents, 0, "\n", "\r\n");
+      base::ReplaceSubstringsAfterOffset(
+          &argfile_default_contents, 0, "\n", "\r\n");
 #endif
       base::CreateDirectory(arg_file.DirName());
       base::WriteFile(arg_file, argfile_default_contents.c_str(),

tools/gn/setup.cc

diff --git a/tools/gn/setup.cc b/tools/gn/setup.cc
index aa8e8f0..033dab4 100644
--- a/tools/gn/setup.cc
+++ b/tools/gn/setup.cc
@@ -370,7 +370,7 @@
 #if defined(OS_WIN)
   // Use Windows lineendings for this file since it will often open in
   // Notepad which can't handle Unix ones.
-  ReplaceSubstringsAfterOffset(&contents, 0, "\n", "\r\n");
+  base::ReplaceSubstringsAfterOffset(&contents, 0, "\n", "\r\n");
 #endif
   if (base::WriteFile(build_arg_file, contents.c_str(),
       static_cast<int>(contents.size())) == -1) {