Revert of base: Avoid unnecessary allocations in base::FindThreadID.

base/linux_util.cc

Index: base/linux_util.cc
diff --git a/base/linux_util.cc b/base/linux_util.cc
index a5e73b2eff2a887b825f5f0a37857cf6aeb9dce6..bf504718f06f2accdfb9656c8714a5ba6c536e9f 100644
--- a/base/linux_util.cc
+++ b/base/linux_util.cc
@@ -22,7 +22,6 @@
 #include "base/process/launch.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/string_split.h"
-#include "base/strings/string_tokenizer.h"
 #include "base/strings/string_util.h"
 #include "base/synchronization/lock.h"
 #include "build/build_config.h"
@@ -200,24 +199,25 @@
     std::string status;
     if (!ReadFileToString(FilePath(buf), &status))
       return -1;
-    StringTokenizer tokenizer(status, "\n");
-    while (tokenizer.GetNext()) {
-      StringPiece value_str(tokenizer.token_piece());
-      if (!value_str.starts_with("NSpid"))
-        continue;
-      if (ns_pid_supported)
-        *ns_pid_supported = true;
-      std::vector<StringPiece> split_value_str = SplitStringPiece(
-          value_str, "\t", TRIM_WHITESPACE, SPLIT_WANT_NONEMPTY);
-      DCHECK_GE(split_value_str.size(), 3u);
-      int value;
-      // The last value in the list is the PID in the namespace.
-      if (StringToInt(split_value_str.back(), &value) && value == ns_tid) {
-        // The second value in the list is the real PID.
-        if (StringToInt(split_value_str[1], &value))
-          return value;
+    StringPairs pairs;
+    SplitStringIntoKeyValuePairs(status, ':', '\n', &pairs);
+    for (const auto& pair : pairs) {
+      const std::string& key = pair.first;
+      const std::string& value_str = pair.second;
+      if (key == "NSpid") {
+        if (ns_pid_supported)
+          *ns_pid_supported = true;
+        std::vector<StringPiece> split_value_str = SplitStringPiece(
+            value_str, "\t", TRIM_WHITESPACE, SPLIT_WANT_NONEMPTY);
+        DCHECK_NE(split_value_str.size(), 0u);
+        int value;
+        // The last value in the list is the PID in the namespace.
+        if (StringToInt(split_value_str.back(), &value) && value == ns_tid) {
+          // The first value in the list is the real PID.
+          if (StringToInt(split_value_str.front(), &value))
+            return value;
+        }
       }
-      break;
     }
   }
   return -1;