Extract hardcoded error strings into a single place and replace them with enum.

src/code-stubs-hydrogen.cc

Index: src/code-stubs-hydrogen.cc
diff --git a/src/code-stubs-hydrogen.cc b/src/code-stubs-hydrogen.cc
index 235950de9cd9d29899b5b8e607a5a71e6ec1b332..934f9a6fa12b1a48ba0b65cc3f4d947f3c32eb4f 100644
--- a/src/code-stubs-hydrogen.cc
+++ b/src/code-stubs-hydrogen.cc
@@ -41,13 +41,13 @@ static LChunk* OptimizeGraph(HGraph* graph) {
   DisallowHandleDereference no_deref;
 
   ASSERT(graph != NULL);
-  SmartArrayPointer<char> bailout_reason;
+  BailoutReason bailout_reason = kNoReason;
   if (!graph->Optimize(&bailout_reason)) {
-    FATAL(bailout_reason.is_empty() ? "unknown" : *bailout_reason);
+    FATAL(GetBailoutReason(bailout_reason));
   }
   LChunk* chunk = LChunk::NewChunk(graph);
   if (chunk == NULL) {
-    FATAL(graph->info()->bailout_reason());
+    FATAL(GetBailoutReason(graph->info()->bailout_reason()));
   }
   return chunk;
 }