Make list constructor usable without list-inl.h header.

src/list.h

Index: src/list.h
diff --git a/src/list.h b/src/list.h
index 8021a9fbed1e5d955cbf910107f1c26d948ab5f6..d935f764b86efd97fd70d257b58ac39f87ac848e 100644
--- a/src/list.h
+++ b/src/list.h
@@ -166,7 +166,12 @@ class List {
   void StableSort();
 
   INLINE(void Initialize(int capacity,
-                         AllocationPolicy allocator = AllocationPolicy()));
+                         AllocationPolicy allocator = AllocationPolicy())) {
+    DCHECK(capacity >= 0);
+    data_ = (capacity > 0) ? NewData(capacity, allocator) : NULL;
+    capacity_ = capacity;
+    length_ = 0;
+  }
 
  private:
   T* data_;