[builtins] Provide Math.floor as TurboFan builtin.

src/builtins.h

Index: src/builtins.h
diff --git a/src/builtins.h b/src/builtins.h
index f3a5deccf2e6edef51c01e16f54e119bddeb27bf..6554c34d3ff750836cf96a97c739ef381e36e36c 100644
--- a/src/builtins.h
+++ b/src/builtins.h
@@ -307,7 +307,9 @@ inline bool operator&(BuiltinExtraArguments lhs, BuiltinExtraArguments rhs) {
   CODE_AGE_LIST_WITH_ARG(DECLARE_CODE_AGE_BUILTIN, V)
 
 // Define list of builtins implemented in TurboFan (with JS linkage).
-#define BUILTIN_LIST_T(V) V(MathSqrt, 2)
+#define BUILTIN_LIST_T(V) \
+  V(MathFloor, 2)         \
+  V(MathSqrt, 2)
 
 // Define list of builtin handlers implemented in assembly.
 #define BUILTIN_LIST_H(V)                    \
@@ -580,6 +582,8 @@ class Builtins {
   static void Generate_InternalArrayCode(MacroAssembler* masm);
   static void Generate_ArrayCode(MacroAssembler* masm);
 
+  // ES6 section 20.2.2.16 Math.floor ( x )
+  static void Generate_MathFloor(compiler::CodeStubAssembler* assembler);
   enum class MathMaxMinKind { kMax, kMin };
   static void Generate_MathMaxMin(MacroAssembler* masm, MathMaxMinKind kind);
   // ES6 section 20.2.2.24 Math.max ( value1, value2 , ...values )