Revert 6996, causes Mozilla debug failures on x64 with crankshaft.

src/x64/lithium-x64.cc

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 1708 matching lines @@
 }
 
 
 LInstruction* LChunkBuilder::DoLoadContextSlot(HLoadContextSlot* instr) {
   LOperand* context = UseRegisterAtStart(instr->value());
   return DefineAsRegister(new LLoadContextSlot(context));
 }
 
 
 LInstruction* LChunkBuilder::DoStoreContextSlot(HStoreContextSlot* instr) {
+  Abort("Unimplemented: DoStoreContextSlot");  // Temporarily disabled (whesse).
   LOperand* context;
   LOperand* value;
   if (instr->NeedsWriteBarrier()) {
     context = UseTempRegister(instr->context());
     value = UseTempRegister(instr->value());
   } else {
     context = UseRegister(instr->context());
     value = UseRegister(instr->value());
   }
   return new LStoreContextSlot(context, value);
@@ skipping 295 matching lines @@
 
 LInstruction* LChunkBuilder::DoLeaveInlined(HLeaveInlined* instr) {
   HEnvironment* outer = current_block_->last_environment()->outer();
   current_block_->UpdateEnvironment(outer);
   return NULL;
 }
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_X64