Test tracing of string allocations

runtime/vm/intrinsifier_arm.cc

Index: runtime/vm/intrinsifier_arm.cc
diff --git a/runtime/vm/intrinsifier_arm.cc b/runtime/vm/intrinsifier_arm.cc
index 0c5ce2c3e3a9fd3f28c23c473bb7b7629f626c7a..893352e82ef9dd3d5c42884b38ec31f095f3f52e 100644
--- a/runtime/vm/intrinsifier_arm.cc
+++ b/runtime/vm/intrinsifier_arm.cc
@@ -1763,7 +1763,7 @@ static void TryAllocateOnebyteString(Assembler* assembler,
                                      Label* failure) {
   const Register length_reg = R2;
   Label fail;
-
+  __ MaybeTraceAllocation(kOneByteStringCid, R0, failure);
   __ mov(R6, Operand(length_reg));  // Save the length register.
   // TODO(koda): Protect against negative length and overflow here.
   __ SmiUntag(length_reg);