[turbofan] Add RegisterAllocator::NewLiveRange() utility method.

src/compiler/register-allocator.h

Index: src/compiler/register-allocator.h
diff --git a/src/compiler/register-allocator.h b/src/compiler/register-allocator.h
index 91d3174cd3622d39a74ec60f83077ab5c945b506..9ee778d0bd358d37a58fcafb1077b6398a376acf 100644
--- a/src/compiler/register-allocator.h
+++ b/src/compiler/register-allocator.h
@@ -470,6 +470,9 @@ class RegisterAllocator FINAL : public ZoneObject {
   // Returns the register kind required by the given virtual register.
   RegisterKind RequiredRegisterKind(int virtual_register) const;
 
+  // Creates a new live range.
+  LiveRange* NewLiveRange(int index);
+
   // This zone is for InstructionOperands and moves that live beyond register
   // allocation.
   Zone* code_zone() const { return code()->zone(); }