Fix off-by-one bug in TurboFan register allocator.

src/compiler/instruction.h

Index: src/compiler/instruction.h
diff --git a/src/compiler/instruction.h b/src/compiler/instruction.h
index fddc225f8a23286a9b8a59a070248c9a3d0843e9..43958b8c6f4e92e0d3a710c05647b3362c6a7590 100644
--- a/src/compiler/instruction.h
+++ b/src/compiler/instruction.h
@@ -862,6 +862,11 @@ class InstructionSequence FINAL {
     return instruction_blocks_[rpo_number.ToSize()];
   }
 
+  int LastLoopInstructionIndex(const InstructionBlock* block) {
+    return instruction_blocks_[block->loop_end().ToSize() - 1]
+        ->last_instruction_index();
+  }
+
   const InstructionBlock* InstructionBlockAt(
       BasicBlock::RpoNumber rpo_number) const {
     return instruction_blocks_[rpo_number.ToSize()];