Valgrind cleanliness, part 6: Introduce OS::TearDown, cleaning up 2 mutexes.

src/platform-linux.cc

Index: src/platform-linux.cc
diff --git a/src/platform-linux.cc b/src/platform-linux.cc
index 9bea32df3a01d46e52adb38885c20cc6b9a79967..bed069dfb79283280a9e50f4c5e247b258d5ca1e 100644
--- a/src/platform-linux.cc
+++ b/src/platform-linux.cc
@@ -1055,11 +1055,8 @@ class SignalSender : public Thread {
         vm_tgid_(getpid()),
         interval_(interval) {}
 
-  static void SetUp() {
-    if (!mutex_) {
-      mutex_ = OS::CreateMutex();
-    }
-  }
+  static void SetUp() { if (!mutex_) mutex_ = OS::CreateMutex(); }
+  static void TearDown() { delete mutex_; }
 
   static void InstallSignalHandler() {
     struct sigaction sa;
@@ -1238,6 +1235,12 @@ void OS::SetUp() {
 }
 
 
+void OS::TearDown() {
+  SignalSender::TearDown();
+  delete limit_mutex;
+}
+
+
 Sampler::Sampler(Isolate* isolate, int interval)
     : isolate_(isolate),
       interval_(interval),