Introduce --log-external-callbacks flag apart from --log-timer-events.

src/arm/macro-assembler-arm.cc

Index: src/arm/macro-assembler-arm.cc
diff --git a/src/arm/macro-assembler-arm.cc b/src/arm/macro-assembler-arm.cc
index 7f6c60d2af60103b3fa0edf8e0a212ea5415bfb7..c34343450f5fceba3e0430980ea8ae0abc3f7c43 100644
--- a/src/arm/macro-assembler-arm.cc
+++ b/src/arm/macro-assembler-arm.cc
@@ -2222,7 +2222,7 @@ void MacroAssembler::CallApiFunctionAndReturn(ExternalReference function,
   add(r6, r6, Operand(1));
   str(r6, MemOperand(r7, kLevelOffset));
 
-  if (FLAG_log_timer_events) {
+  if (FLAG_log_external_callbacks) {
     FrameScope frame(this, StackFrame::MANUAL);
     PushSafepointRegisters();
     PrepareCallCFunction(0, r0);
@@ -2236,7 +2236,7 @@ void MacroAssembler::CallApiFunctionAndReturn(ExternalReference function,
   DirectCEntryStub stub;
   stub.GenerateCall(this, function);
 
-  if (FLAG_log_timer_events) {
+  if (FLAG_log_external_callbacks) {
     FrameScope frame(this, StackFrame::MANUAL);
     PushSafepointRegisters();
     PrepareCallCFunction(0, r0);