Add note why we used a switch.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@174449 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Analysis/CFG.cpp b/lib/Analysis/CFG.cpp
index 1cbaaee..01553b8 100644
--- a/lib/Analysis/CFG.cpp
+++ b/lib/Analysis/CFG.cpp
@@ -251,6 +251,7 @@
     return;
   }
   switch (S->getStmtClass()) {
+    // Note: Fill in this switch with more cases we want to optimize.
     case Stmt::InitListExprClass: {
       InitListExpr *IE = cast<InitListExpr>(S);
       children = llvm::makeArrayRef(reinterpret_cast<Stmt**>(IE->getInits()),