Constify methods.

llvm-svn: 76939
diff --git a/clang/lib/Index/Entity.cpp b/clang/lib/Index/Entity.cpp
index 25061e6..85b4f2e 100644
--- a/clang/lib/Index/Entity.cpp
+++ b/clang/lib/Index/Entity.cpp
@@ -145,7 +145,7 @@
 Entity::Entity(Decl *D) : Val(D->getCanonicalDecl()) { }
 
 /// \brief Find the Decl that can be referred to by this entity.
-Decl *Entity::getDecl(ASTContext &AST) {
+Decl *Entity::getDecl(ASTContext &AST) const {
   if (isInvalid())
     return 0;