x86/x64 port of Math.floor(x/y) to use integer division for specific divisor

src/x64/lithium-x64.h

Index: src/x64/lithium-x64.h
===================================================================
--- src/x64/lithium-x64.h	(revision 11883)
+++ src/x64/lithium-x64.h	(working copy)
@@ -132,6 +132,7 @@
   V(LoadNamedField)                             \
   V(LoadNamedFieldPolymorphic)                  \
   V(LoadNamedGeneric)                           \
+  V(MathFloorOfDiv)                             \
   V(ModI)                                       \
   V(MulI)                                       \
   V(NumberTagD)                                 \
@@ -554,6 +555,21 @@
 };
 
 
+class LMathFloorOfDiv: public LTemplateInstruction<1, 2, 1> {
+ public:
+  LMathFloorOfDiv(LOperand* left,
+                  LOperand* right,
+                  LOperand* temp = NULL) {
+    inputs_[0] = left;
+    inputs_[1] = right;
+    temps_[0] = temp;
+  }
+
+  DECLARE_CONCRETE_INSTRUCTION(MathFloorOfDiv, "math-floor-of-div")
+  DECLARE_HYDROGEN_ACCESSOR(MathFloorOfDiv)
+};
+
+
 class LMulI: public LTemplateInstruction<1, 2, 0> {
  public:
   LMulI(LOperand* left, LOperand* right) {
@@ -2255,6 +2271,9 @@
   HYDROGEN_CONCRETE_INSTRUCTION_LIST(DECLARE_DO)
 #undef DECLARE_DO
 
+  static HValue* SimplifiedDividendForMathFloorOfDiv(HValue* val);
+  static HValue* SimplifiedDivisorForMathFloorOfDiv(HValue* val);
+
  private:
   enum Status {
     UNUSED,