Ensure that scanner state is correctly reset when an error is encountered.

src/utils.h

Index: src/utils.h
diff --git a/src/utils.h b/src/utils.h
index 8eddb1391d15ff1e6fd5db12d81f531eeeaac34a..90fa74f9fb0e43c4ced4e182e4b0263b03a12447 100644
--- a/src/utils.h
+++ b/src/utils.h
@@ -560,6 +560,15 @@ class Collector {
     return Vector<T>(new_store, total_length);
   }
 
+  // Resets the collector to be empty.
+  virtual void Reset() {
+    for (int i = chunks_.length() - 1; i >= 0; i--) {
+      chunks_.at(i).Dispose();
+    }
+    chunks_.Rewind(0);
+    index_ = 0;
+  }
+
  protected:
   static const int kMinCapacity = 16;
   List<Vector<T> > chunks_;
@@ -632,6 +641,18 @@ class SequenceCollector : public Collector<T> {
                      this->index_ - sequence_start);
   }
 
+  // Drops the currently added sequence, and all collected elements in it.
+  void DropSequence() {
+    ASSERT(sequence_start_ != kNoSequence);
+    this->index_ = sequence_start_;
+    sequence_start_ = kNoSequence;
+  }
+
+  virtual void Reset() {
+    sequence_start_ = kNoSequence;
+    this->Collector<T>::Reset();
+  }
+
  private:
   static const int kNoSequence = -1;
   int sequence_start_;