Deoptimize context value in Turbofan (and Crankshaft).

src/compiler/graph-builder.h

Index: src/compiler/graph-builder.h
diff --git a/src/compiler/graph-builder.h b/src/compiler/graph-builder.h
index dfa79b8684b4e83509cea0d2de78d9fe72ccf264..398939b3b159e6699ca43848448739804957ab83 100644
--- a/src/compiler/graph-builder.h
+++ b/src/compiler/graph-builder.h
@@ -101,6 +101,7 @@ class StructuredGraphBuilder : public GraphBuilder {
 
  protected:
   class Environment;
+  friend class Environment;
   friend class ControlBuilder;
 
   // The following method creates a new node having the specified operator and
@@ -202,6 +203,8 @@ class StructuredGraphBuilder::Environment : public ZoneObject {
     return builder()->CopyEnvironment(this);
   }
 
+  Node* GetContext() { return builder_->current_context(); }
+
  protected:
   // TODO(mstarzinger): Use phase-local zone instead!
   Zone* zone() const { return graph()->zone(); }