A64: Synchronize with r16489.

src/assembler.cc

Index: src/assembler.cc
diff --git a/src/assembler.cc b/src/assembler.cc
index 34ad78ef07c85feb4fbf88aee6b26fbc933b3b33..7c5cffacaf141c9fca9d0cd0d66665ff43bacb21 100644
--- a/src/assembler.cc
+++ b/src/assembler.cc
@@ -894,7 +894,7 @@ void ExternalReference::SetUp() {
   double_constants.the_hole_nan = BitCast<double>(kHoleNanInt64);
   double_constants.negative_infinity = -V8_INFINITY;
 
-  math_exp_data_mutex = OS::CreateMutex();
+  math_exp_data_mutex = new Mutex();
 }
 
 
@@ -902,7 +902,7 @@ void ExternalReference::InitializeMathExpData() {
   // Early return?
   if (math_exp_data_initialized) return;
 
-  math_exp_data_mutex->Lock();
+  LockGuard<Mutex> lock_guard(math_exp_data_mutex);
   if (!math_exp_data_initialized) {
     // If this is changed, generated code must be adapted too.
     const int kTableSizeBits = 11;
@@ -938,7 +938,6 @@ void ExternalReference::InitializeMathExpData() {
 
     math_exp_data_initialized = true;
   }
-  math_exp_data_mutex->Unlock();
 }