Fully qualify std::string

PiperOrigin-RevId: 364483152
Change-Id: Iee5738c7447306670919ef25f61d2d13571ed763
diff --git a/tensorflow/core/platform/base64.cc b/tensorflow/core/platform/base64.cc
index 8e22e61..b8f3698 100644
--- a/tensorflow/core/platform/base64.cc
+++ b/tensorflow/core/platform/base64.cc
@@ -194,10 +194,12 @@
   return Status::OK();
 }
 
-template Status Base64Decode<string>(StringPiece data, string* decoded);
-template Status Base64Encode<string>(StringPiece source, string* encoded);
-template Status Base64Encode<string>(StringPiece source, bool with_padding,
-                                     string* encoded);
+template Status Base64Decode<std::string>(StringPiece data,
+                                          std::string* decoded);
+template Status Base64Encode<std::string>(StringPiece source,
+                                          std::string* encoded);
+template Status Base64Encode<std::string>(StringPiece source, bool with_padding,
+                                          std::string* encoded);
 
 template Status Base64Decode<tstring>(StringPiece data, tstring* decoded);
 template Status Base64Encode<tstring>(StringPiece source, tstring* encoded);
diff --git a/tensorflow/core/platform/base64.h b/tensorflow/core/platform/base64.h
index 4228894..ff13727 100644
--- a/tensorflow/core/platform/base64.h
+++ b/tensorflow/core/platform/base64.h
@@ -37,11 +37,13 @@
 Status Base64Decode(StringPiece data, T* decoded);
 
 // Explicit instantiations defined in base64.cc.
-extern template Status Base64Decode<string>(StringPiece data, string* decoded);
-extern template Status Base64Encode<string>(StringPiece source,
-                                            string* encoded);
-extern template Status Base64Encode<string>(StringPiece source,
-                                            bool with_padding, string* encoded);
+extern template Status Base64Decode<std::string>(StringPiece data,
+                                                 std::string* decoded);
+extern template Status Base64Encode<std::string>(StringPiece source,
+                                                 std::string* encoded);
+extern template Status Base64Encode<std::string>(StringPiece source,
+                                                 bool with_padding,
+                                                 std::string* encoded);
 
 extern template Status Base64Decode<tstring>(StringPiece data,
                                              tstring* decoded);
diff --git a/tensorflow/core/platform/numbers.cc b/tensorflow/core/platform/numbers.cc
index e96ef62..606759e 100644
--- a/tensorflow/core/platform/numbers.cc
+++ b/tensorflow/core/platform/numbers.cc
@@ -37,9 +37,9 @@
 namespace {
 
 template <typename T>
-const std::unordered_map<string, T>* GetSpecialNumsSingleton() {
-  static const std::unordered_map<string, T>* special_nums =
-      CHECK_NOTNULL((new const std::unordered_map<string, T>{
+const std::unordered_map<std::string, T>* GetSpecialNumsSingleton() {
+  static const std::unordered_map<std::string, T>* special_nums =
+      CHECK_NOTNULL((new const std::unordered_map<std::string, T>{
           {"inf", std::numeric_limits<T>::infinity()},
           {"+inf", std::numeric_limits<T>::infinity()},
           {"-inf", -std::numeric_limits<T>::infinity()},
@@ -59,7 +59,7 @@
   std::stringstream s(str);
 
   // Check if str is one of the special numbers.
-  string special_num_str;
+  std::string special_num_str;
   s >> special_num_str;
 
   for (size_t i = 0; i < special_num_str.length(); ++i) {
@@ -399,13 +399,13 @@
   return snprintf_result;
 }
 
-string FpToString(Fprint fp) {
+std::string FpToString(Fprint fp) {
   char buf[17];
   snprintf(buf, sizeof(buf), "%016llx", static_cast<long long>(fp));
-  return string(buf);
+  return std::string(buf);
 }
 
-bool StringToFp(const string& s, Fprint* fp) {
+bool StringToFp(const std::string& s, Fprint* fp) {
   char junk;
   uint64_t result;
   if (sscanf(s.c_str(), "%" SCNx64 "%c", &result, &junk) == 1) {
@@ -448,8 +448,8 @@
   return true;
 }
 
-string HumanReadableNum(int64 value) {
-  string s;
+std::string HumanReadableNum(int64 value) {
+  std::string s;
   if (value < 0) {
     s += "-";
     value = -value;
@@ -472,7 +472,7 @@
   return s;
 }
 
-string HumanReadableNumBytes(int64 num_bytes) {
+std::string HumanReadableNumBytes(int64 num_bytes) {
   if (num_bytes == kint64min) {
     // Special case for number with not representable negation.
     return "-8E";
@@ -489,7 +489,7 @@
     char buf[8];  // Longest possible string is '-XXXXB'
     snprintf(buf, sizeof(buf), "%s%lldB", neg_str,
              static_cast<long long>(num_bytes));
-    return string(buf);
+    return std::string(buf);
   }
 
   static const char units[] = "KMGTPE";  // int64 only goes up to E.
@@ -504,11 +504,11 @@
   char buf[16];
   snprintf(buf, sizeof(buf), ((*unit == 'K') ? "%s%.1f%ciB" : "%s%.2f%ciB"),
            neg_str, num_bytes / 1024.0, *unit);
-  return string(buf);
+  return std::string(buf);
 }
 
-string HumanReadableElapsedTime(double seconds) {
-  string human_readable;
+std::string HumanReadableElapsedTime(double seconds) {
+  std::string human_readable;
 
   if (seconds < 0) {
     human_readable = "-";