[turbofan] Treat uninitialized source positions as unknown.

src/compiler/instruction.cc

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/compiler/common-operator.h"
 #include "src/compiler/graph.h"
 #include "src/compiler/instruction.h"
 #include "src/compiler/schedule.h"
 
 namespace v8 {
@@ skipping 639 matching lines @@
                                             SourcePosition* result) const {
   auto it = source_positions_.find(instr);
   if (it == source_positions_.end()) return false;
   *result = it->second;
   return true;
 }
 
 
 void InstructionSequence::SetSourcePosition(const Instruction* instr,
                                             SourcePosition value) {
-  DCHECK(!value.IsInvalid());
-  DCHECK(!value.IsUnknown());
   source_positions_.insert(std::make_pair(instr, value));
 }
 
 
 FrameStateDescriptor::FrameStateDescriptor(
     Zone* zone, const FrameStateCallInfo& state_info, size_t parameters_count,
     size_t locals_count, size_t stack_count, FrameStateDescriptor* outer_state)
     : type_(state_info.type()),
       bailout_id_(state_info.bailout_id()),
       frame_state_combine_(state_info.state_combine()),
@@ skipping 128 matching lines @@
       os << " B" << succ.ToInt();
     }
     os << "\n";
   }
   return os;
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8