ARM: Implement DoMathRound in the lithium code generator.

src/arm/lithium-arm.cc

Index: src/arm/lithium-arm.cc
diff --git a/src/arm/lithium-arm.cc b/src/arm/lithium-arm.cc
index 786ceeb3cac0b52afa0500645679d174ee08ca5d..d02b337371418437aab33727727c3efbd5e35fa6 100644
--- a/src/arm/lithium-arm.cc
+++ b/src/arm/lithium-arm.cc
@@ -1204,8 +1204,7 @@ LInstruction* LChunkBuilder::DoUnaryMathOperation(HUnaryMathOperation* instr) {
     case kMathSqrt:
       return DefineSameAsFirst(result);
     case kMathRound:
-      Abort("MathRound LUnaryMathOperation not implemented");
-      return NULL;
+      return AssignEnvironment(DefineAsRegister(result));
     case kMathPowHalf:
       Abort("MathPowHalf LUnaryMathOperation not implemented");
       return NULL;