Revert "Remove a pointless assertion."

This reverts commit r177158.

I'm blindly reverting this because it appears to be breaking numerous
buildbots.  I'll reapply if it doesn't turn out to be the culprit.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@177165 91177308-0d34-0410-b5e6-96231b3b80d8

lib/AST/ASTContext.cpp

@@ -2026,9 +2026,13 @@ QualType ASTContext::getPointerType(QualType T) const {
   // If the pointee type isn't canonical, this won't be a canonical type either,
   // so fill in the canonical type field.
   QualType Canonical;
-  if (!T.isCanonical())
+  if (!T.isCanonical()) {
     Canonical = getPointerType(getCanonicalType(T));
 
+    // Get the new insert position for the node we care about.
+    PointerType *NewIP = PointerTypes.FindNodeOrInsertPos(ID, InsertPos);
+    assert(NewIP == 0 && "Shouldn't be in the map!"); (void)NewIP;
+  }
   PointerType *New = new (*this, TypeAlignment) PointerType(T, Canonical);
   Types.push_back(New);
   PointerTypes.InsertNode(New, InsertPos);