Update ReadProcMaps() to reflect lack of atomicity when reading /proc/self/maps.

base/debug/proc_maps_linux_unittest.cc

Index: base/debug/proc_maps_linux_unittest.cc
diff --git a/base/debug/proc_maps_linux_unittest.cc b/base/debug/proc_maps_linux_unittest.cc
index 9b7d7dcc4af3419c1ef0078eec4007f3fec804fa..6a043b88d0a2b850af6bb0dc61fbb0e65d4ba915 100644
--- a/base/debug/proc_maps_linux_unittest.cc
+++ b/base/debug/proc_maps_linux_unittest.cc
@@ -180,14 +180,7 @@ TEST(ProcMapsTest, Permissions) {
   }
 }
 
-// ProcMapsTest.ReadProcMaps fails under TSan on Linux,
-// see http://crbug.com/258451.
-#if defined(THREAD_SANITIZER)
-#define MAYBE_ReadProcMaps DISABLED_ReadProcMaps
-#else
-#define MAYBE_ReadProcMaps ReadProcMaps
-#endif
-TEST(ProcMapsTest, MAYBE_ReadProcMaps) {
+TEST(ProcMapsTest, ReadProcMaps) {
   std::string proc_maps;
   ASSERT_TRUE(ReadProcMaps(&proc_maps));