Migrate ignore_result to std::ignore (see issue #3234)

See https://crbug.com/1285085 for background.

include/base/cef_compiler_specific.h

@@ -156,7 +156,7 @@
 // Annotate a function indicating the caller must examine the return value.
 // Use like:
 //   int foo() WARN_UNUSED_RESULT;
-// To explicitly ignore a result, see |ignore_result()| in base/macros.h.
+// To explicitly ignore a result, use std::ignore from <tuple>.
 #undef WARN_UNUSED_RESULT
 #if defined(COMPILER_GCC) || defined(__clang__)
 #define WARN_UNUSED_RESULT __attribute__((warn_unused_result))

include/base/cef_macros.h

@@ -32,11 +32,7 @@
 #define CEF_INCLUDE_BASE_CEF_MACROS_H_
 #pragma once
 
-#if defined(USING_CHROMIUM_INCLUDES)
-// When building CEF include the Chromium header directly.
-#include "base/ignore_result.h"
-
-#else  // !USING_CHROMIUM_INCLUDES
+#if !defined(USING_CHROMIUM_INCLUDES)
 // The following is substantially similar to the Chromium implementation.
 // If the Chromium implementation diverges the below implementation should be
 // updated to match.
@@ -62,17 +58,6 @@
   TypeName() = delete;                           \
   DISALLOW_COPY_AND_ASSIGN(TypeName)
 
-// Used to explicitly mark the return value of a function as unused. If you are
-// really sure you don't want to do anything with the return value of a function
-// that has been marked WARN_UNUSED_RESULT, wrap it with this. Example:
-//
-//   std::unique_ptr<MyType> my_var = ...;
-//   if (TakeOwnership(my_var.get()) == SUCCESS)
-//     ignore_result(my_var.release());
-//
-template <typename T>
-inline void ignore_result(const T&) {}
-
 #endif  // !USING_CHROMIUM_INCLUDES
 
 #endif  // CEF_INCLUDE_BASE_CEF_MACROS_H_