Fix potential overwriting of debug jumps of following code.

src/x64/macro-assembler-x64.h

Index: src/x64/macro-assembler-x64.h
diff --git a/src/x64/macro-assembler-x64.h b/src/x64/macro-assembler-x64.h
index 35369118751d8ff4faca4577305cd0f101e9a296..195ee364e1d4d47e3b060af618b2319f96fa076d 100644
--- a/src/x64/macro-assembler-x64.h
+++ b/src/x64/macro-assembler-x64.h
@@ -74,7 +74,7 @@ class MacroAssembler: public Assembler {
 
   void LoadRoot(Register destination, Heap::RootListIndex index);
   void CompareRoot(Register with, Heap::RootListIndex index);
-  void CompareRoot(Operand with, Heap::RootListIndex index);
+  void CompareRoot(const Operand& with, Heap::RootListIndex index);
   void PushRoot(Heap::RootListIndex index);
   void StoreRoot(Register source, Heap::RootListIndex index);
 
@@ -596,6 +596,12 @@ class MacroAssembler: public Assembler {
   void Call(ExternalReference ext);
   void Call(Handle<Code> code_object, RelocInfo::Mode rmode);
 
+  // Emit call to the code we are currently generating.
+  void CallSelf() {
+    Handle<Code> self(reinterpret_cast<Code**>(CodeObject().location()));
+    Call(self, RelocInfo::CODE_TARGET);
+  }
+
   // Non-x64 instructions.
   // Push/pop all general purpose registers.
   // Does not push rsp/rbp nor any of the assembler's special purpose registers
@@ -1772,6 +1778,23 @@ void MacroAssembler::InvokePrologue(const ParameterCount& expected,
 }
 
 
+// Ensures that code is padded to at least a given size.
+class Padding BASE_EMBEDDED {
+ public:
+  Padding(Assembler* masm, int min_size)
+      : masm_(masm), min_end_offset_(masm->pc_offset() + min_size) { }
+  ~Padding() {
+    int offset = masm_->pc_offset();
+    if (offset < min_end_offset_) {
+      masm_->Pad(min_end_offset_ - offset);
+    }
+  }
+ private:
+  Assembler* masm_;
+  int min_end_offset_;
+};
+
+
 } }  // namespace v8::internal
 
 #endif  // V8_X64_MACRO_ASSEMBLER_X64_H_