Fix an overflow in on-stack replacement spill-slot allocation for Crankshaft.

src/x64/lithium-x64.cc

Index: src/x64/lithium-x64.cc
diff --git a/src/x64/lithium-x64.cc b/src/x64/lithium-x64.cc
index c0b4657b6c53db3d81765598a5912c3b807d095e..1571d62b25f1da38a450d6b10f5a56173ecedf49 100644
--- a/src/x64/lithium-x64.cc
+++ b/src/x64/lithium-x64.cc
@@ -2112,6 +2112,9 @@ LInstruction* LChunkBuilder::DoParameter(HParameter* instr) {
 
 LInstruction* LChunkBuilder::DoUnknownOSRValue(HUnknownOSRValue* instr) {
   int spill_index = chunk()->GetNextSpillIndex(false);  // Not double-width.
+  if (spill_index > LUnallocated::kMaxFixedIndex) {
+    Abort("Too many spill slots needed for OSR");
+  }
   return DefineAsSpilled(new LUnknownOSRValue, spill_index);
 }