[turbofan] Implemented the ChangeFloat64ToInt64 TurboFan operator.

src/compiler/mips64/code-generator-mips64.cc

Index: src/compiler/mips64/code-generator-mips64.cc
diff --git a/src/compiler/mips64/code-generator-mips64.cc b/src/compiler/mips64/code-generator-mips64.cc
index b67302ef90794cea1bed78571c4b720502c78b31..6591fbfc9bb821d81aab2e71e81afad00b45fef2 100644
--- a/src/compiler/mips64/code-generator-mips64.cc
+++ b/src/compiler/mips64/code-generator-mips64.cc
@@ -974,6 +974,13 @@ void CodeGenerator::AssembleArchInstruction(Instruction* instr) {
       __ mfc1(i.OutputRegister(), scratch);
       break;
     }
+    case kMips64TruncLD: {
+      FPURegister scratch = kScratchDoubleReg;
+      // Other arches use round to zero here, so we follow.
+      __ trunc_l_d(scratch, i.InputDoubleRegister(0));
+      __ dmfc1(i.OutputRegister(), scratch);
+      break;
+    }
     case kMips64TruncUwD: {
       FPURegister scratch = kScratchDoubleReg;
       // TODO(plind): Fix wrong param order of Trunc_uw_d() macro-asm function.