[turbofan] Keep AstGraphBuilder context chain length in sync.

src/compiler/ast-graph-builder.h

Index: src/compiler/ast-graph-builder.h
diff --git a/src/compiler/ast-graph-builder.h b/src/compiler/ast-graph-builder.h
index f851a3003665bb85f1f1e343e664352dbcb415d3..45f7451652da34fb40d3d18c6cc49d860ecc832d 100644
--- a/src/compiler/ast-graph-builder.h
+++ b/src/compiler/ast-graph-builder.h
@@ -384,6 +384,7 @@ class AstGraphBuilder::Environment : public ZoneObject {
 
   int parameters_count() const { return parameters_count_; }
   int locals_count() const { return locals_count_; }
+  int context_chain_length() { return static_cast<int>(contexts_.size()); }
   int stack_height() {
     return static_cast<int>(values()->size()) - parameters_count_ -
            locals_count_;
@@ -394,9 +395,13 @@ class AstGraphBuilder::Environment : public ZoneObject {
   Node* Lookup(Variable* variable);
   void MarkAllLocalsLive();
 
+  // Operations on the context chain.
   Node* Context() const { return contexts_.back(); }
   void PushContext(Node* context) { contexts()->push_back(context); }
   void PopContext() { contexts()->pop_back(); }
+  void TrimContextChain(int trim_to_length) {
+    contexts()->resize(trim_to_length);
+  }
 
   // Operations on the operand stack.
   void Push(Node* node) {
@@ -428,7 +433,7 @@ class AstGraphBuilder::Environment : public ZoneObject {
     DCHECK(depth >= 0 && depth <= stack_height());
     values()->erase(values()->end() - depth, values()->end());
   }
-  void Trim(int trim_to_height) {
+  void TrimStack(int trim_to_height) {
     int depth = stack_height() - trim_to_height;
     DCHECK(depth >= 0 && depth <= stack_height());
     values()->erase(values()->end() - depth, values()->end());
@@ -478,8 +483,6 @@ class AstGraphBuilder::Environment : public ZoneObject {
     return CopyAndShareLiveness();
   }
 
-  int ContextStackDepth() { return static_cast<int>(contexts_.size()); }
-
  private:
   AstGraphBuilder* builder_;
   int parameters_count_;