New linear scan allocator.

runtime/vm/growable_array.h

Index: runtime/vm/growable_array.h
diff --git a/runtime/vm/growable_array.h b/runtime/vm/growable_array.h
index 2a7fd98be540b81d4a65c51d446fb5376cb47e66..9c472e78f97aabf065df28d0573a129f1f353bd6 100644
--- a/runtime/vm/growable_array.h
+++ b/runtime/vm/growable_array.h
@@ -36,6 +36,11 @@ class BaseGrowableArray : public B {
   T* data() const { return data_; }
   bool is_empty() const { return length_ == 0; }
 
+  void TruncateTo(intptr_t length) {
+    ASSERT(length_ >= length);
+    length_ = length;
+  }
+
   void Add(const T& value) {
     Resize(length() + 1);
     Last() = value;