Take care another assert:

struct A {
  struct B;
};

struct A::B {
  void m() {} // Assertion failed: getContainingDC(DC) == CurContext && "The next DeclContext should be lexically contained in the current one."
};

Introduce DeclContext::getLexicalParent which may be different from DeclContext::getParent when nested-names are involved, e.g:

   namespace A {
      struct S;
   }
   struct A::S {}; // getParent() == namespace 'A'
                   // getLexicalParent() == translation unit

llvm-svn: 59650