Support lazy parsing of inner functions

src/vector.h

Index: src/vector.h
diff --git a/src/vector.h b/src/vector.h
index a4fdb1060efa195056e5c9c6e7df11065c4e584a..5f4fa5439e82a339f103d239071781b0ddfda44d 100644
--- a/src/vector.h
+++ b/src/vector.h
@@ -32,7 +32,7 @@ class Vector {
   // spanning from and including 'from', to but not including 'to'.
   Vector<T> SubVector(int from, int to) {
     SLOW_DCHECK(to <= length_);
-    SLOW_DCHECK(from < to);
+    SLOW_DCHECK(from <= to);
     DCHECK(0 <= from);
     return Vector<T>(start() + from, to - from);
   }
@@ -91,10 +91,17 @@ class Vector {
   }
 
   inline Vector<T> operator+(int offset) {
-    DCHECK(offset < length_);
+    DCHECK(offset <= length_);
     return Vector<T>(start_ + offset, length_ - offset);
   }
 
+  inline Vector<T>& operator+=(int offset) {
+    DCHECK(offset <= length_);
+    start_ += offset;
+    length_ -= offset;
+    return *this;
+  }
+
   // Factory method for creating empty vectors.
   static Vector<T> empty() { return Vector<T>(NULL, 0); }