[interpreter] Move temporary register allocator into own file.

src/identity-map.cc

Index: src/identity-map.cc
diff --git a/src/identity-map.cc b/src/identity-map.cc
index 723cdfa2a6427d52ea20d9381c44360f0b85b050..2f5739dad99341031c4ade37182c82636dfe4c87 100644
--- a/src/identity-map.cc
+++ b/src/identity-map.cc
@@ -14,11 +14,18 @@ namespace internal {
 static const int kInitialIdentityMapSize = 4;
 static const int kResizeFactor = 4;
 
-IdentityMapBase::~IdentityMapBase() {
-  if (keys_) heap_->UnregisterStrongRoots(keys_);
+IdentityMapBase::~IdentityMapBase() { Clear(); }
+
+void IdentityMapBase::Clear() {
+  if (keys_) {
+    heap_->UnregisterStrongRoots(keys_);
+    keys_ = nullptr;
+    values_ = nullptr;
+    size_ = 0;
+    mask_ = 0;
+  }
 }
 
-
 IdentityMapBase::RawEntry IdentityMapBase::Lookup(Object* key) {
   int index = LookupIndex(key);
   return index >= 0 ? &values_[index] : nullptr;