[builtins] Introduce proper Float64Tan operator.

src/crankshaft/mips64/lithium-mips64.cc

Index: src/crankshaft/mips64/lithium-mips64.cc
diff --git a/src/crankshaft/mips64/lithium-mips64.cc b/src/crankshaft/mips64/lithium-mips64.cc
index 67c7882c5347985f578b256ac68c1d6192d0ef34..89806070873c4e52558c3eeb220a20f83c846a0d 100644
--- a/src/crankshaft/mips64/lithium-mips64.cc
+++ b/src/crankshaft/mips64/lithium-mips64.cc
@@ -1937,13 +1937,6 @@ LInstruction* LChunkBuilder::DoDoubleBits(HDoubleBits* instr) {
 }
 
 
-LInstruction* LChunkBuilder::DoConstructDouble(HConstructDouble* instr) {
-  LOperand* lo = UseRegister(instr->lo());
-  LOperand* hi = UseRegister(instr->hi());
-  return DefineAsRegister(new(zone()) LConstructDouble(hi, lo));
-}
-
-
 LInstruction* LChunkBuilder::DoReturn(HReturn* instr) {
   LOperand* context = info()->IsStub()
       ? UseFixed(instr->context(), cp)