Minor new comments to call graph header.

Break up sections of major functionality with comments.

Swift SVN r26092

include/swift/SILAnalysis/CallGraphAnalysis.h

@@ -257,6 +257,9 @@ public:
   CallGraph(SILModule *M, bool completeModule);
   ~CallGraph();
 
+  // Query funtions for getting roots, nodes, and edges from the call
+  // graph.
+
   ArrayRef<CallGraphNode *> getCallGraphRoots() {
     return CallGraphRoots;
   }
@@ -287,6 +290,9 @@ public:
     return const_cast<CallGraph *>(this)->getCallGraphEdge(AI);
   }
 
+  // Functions for getting bottom-up lists of SCCs or functions in the
+  // call graph.
+
   ArrayRef<CallGraphSCC *> getBottomUpSCCOrder() {
     if (BottomUpSCCOrder.empty())
       computeBottomUpSCCOrder();