Replace OStream with std::ostream.

src/compiler/simplified-operator.h

Index: src/compiler/simplified-operator.h
diff --git a/src/compiler/simplified-operator.h b/src/compiler/simplified-operator.h
index 32f0e8b1b7da4dd4289ff0af67e22f8cfca255b1..2329b4b896ea556a08c48ee117d802352f4ae87e 100644
--- a/src/compiler/simplified-operator.h
+++ b/src/compiler/simplified-operator.h
@@ -28,7 +28,7 @@ struct SimplifiedOperatorBuilderImpl;
 
 enum BaseTaggedness { kUntaggedBase, kTaggedBase };
 
-OStream& operator<<(OStream&, BaseTaggedness);
+std::ostream& operator<<(std::ostream&, BaseTaggedness);
 
 // An access descriptor for loads/stores of fixed structures like field
 // accesses of heap objects. Accesses from either tagged or untagged base
@@ -60,7 +60,7 @@ struct ElementAccess {
 bool operator==(ElementAccess const& lhs, ElementAccess const& rhs);
 bool operator!=(ElementAccess const& lhs, ElementAccess const& rhs);
 
-OStream& operator<<(OStream&, ElementAccess const&);
+std::ostream& operator<<(std::ostream&, ElementAccess const&);
 
 
 // If the accessed object is not a heap object, add this to the header_size.