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..7c2929f212a7ae60d16c5a9282053a541ca302a0 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));
 
@@ -238,6 +231,13 @@ TEST(ProcMapsTest, MAYBE_ReadProcMaps) {
   EXPECT_TRUE(found_address);
 }
 
+TEST(ProcMapsTest, ReadProcMapsNonEmptyString) {
+  std::string old_string("I forgot to clear the string");
+  std::string proc_maps(old_string);
+  ASSERT_TRUE(ReadProcMaps(&proc_maps));
+  EXPECT_EQ(std::string::npos, proc_maps.find(old_string));
+}
+
 TEST(ProcMapsTest, MissingFields) {
   static const char* kTestCases[] = {
     "00400000\n",                               // Missing end + beyond.