Reuse base::EmptyString in GURL implementation.

Also update base::EmptyString to use base::NoDestructor.

Change-Id: I5004a7c4881af0dd7e499ccae59df4cab0369e87
Reviewed-on: https://chromium-review.googlesource.com/1162989Reviewed-by: Lei Zhang <thestig@chromium.org>
Commit-Queue: Daniel Cheng <dcheng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#580744}

base/strings/string_util.cc

@@ -22,7 +22,7 @@
 
 #include "base/logging.h"
 #include "base/macros.h"
-#include "base/memory/singleton.h"
+#include "base/no_destructor.h"
 #include "base/strings/utf_string_conversion_utils.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/third_party/icu/icu_utf.h"
@@ -32,19 +32,6 @@ namespace base {
 
 namespace {
 
-// Force the singleton used by EmptyString[16] to be a unique type. This
-// prevents other code that might accidentally use Singleton<string> from
-// getting our internal one.
-struct EmptyStrings {
-  EmptyStrings() = default;
-  const std::string s;
-  const string16 s16;
-
-  static EmptyStrings* GetInstance() {
-    return Singleton<EmptyStrings>::get();
-  }
-};
-
 // Used by ReplaceStringPlaceholders to track the position in the string of
 // replaced parameters.
 struct ReplacementOffset {
@@ -238,11 +225,13 @@ bool EqualsCaseInsensitiveASCII(StringPiece16 a, StringPiece16 b) {
 }
 
 const std::string& EmptyString() {
-  return EmptyStrings::GetInstance()->s;
+  static const base::NoDestructor<std::string> s;
+  return *s;
 }
 
 const string16& EmptyString16() {
-  return EmptyStrings::GetInstance()->s16;
+  static const base::NoDestructor<string16> s16;
+  return *s16;
 }
 
 template <class StringType>

base/strings/string_util.h

@@ -147,8 +147,8 @@ BASE_EXPORT bool EqualsCaseInsensitiveASCII(StringPiece16 a, StringPiece16 b);
 // strings.
 //
 // It is likely faster to construct a new empty string object (just a few
-// instructions to set the length to 0) than to get the empty string singleton
-// returned by these functions (which requires threadsafe singleton access).
+// instructions to set the length to 0) than to get the empty string instance
+// returned by these functions (which requires threadsafe static access).
 //
 // Therefore, DO NOT USE THESE AS A GENERAL-PURPOSE SUBSTITUTE FOR DEFAULT
 // CONSTRUCTORS. There is only one case where you should use these: functions

url/gurl.cc

@@ -19,8 +19,6 @@
 
 namespace {
 
-static base::LazyInstance<std::string>::Leaky empty_string =
-    LAZY_INSTANCE_INITIALIZER;
 static base::LazyInstance<GURL>::Leaky empty_gurl = LAZY_INSTANCE_INITIALIZER;
 
 }  // namespace
@@ -166,7 +164,7 @@ const std::string& GURL::spec() const {
     return spec_;
 
   DCHECK(false) << "Trying to get the spec of an invalid URL!";
-  return empty_string.Get();
+  return base::EmptyString();
 }
 
 bool GURL::operator<(const GURL& other) const {