[debugger] Ensure at least one breakable position per function.

src/debug/debug.cc

 // Copyright 2012 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/debug/debug.h"
 
 #include "src/api.h"
 #include "src/arguments.h"
 #include "src/bootstrapper.h"
 #include "src/code-stubs.h"
@@ skipping 80 matching lines @@
   } else {
     return 0;
   }
 }
 
 BreakLocation::CodeIterator::CodeIterator(Handle<DebugInfo> debug_info,
                                           BreakLocatorType type)
     : Iterator(debug_info),
       reloc_iterator_(debug_info->abstract_code()->GetCode(),
                       GetModeMask(type)) {
-  if (!Done()) Next();
+  // There is at least one break location.
+  DCHECK(!Done());
+  Next();
 }
 
 int BreakLocation::CodeIterator::GetModeMask(BreakLocatorType type) {
   int mask = 0;
   mask |= RelocInfo::ModeMask(RelocInfo::POSITION);
   mask |= RelocInfo::ModeMask(RelocInfo::STATEMENT_POSITION);
   mask |= RelocInfo::ModeMask(RelocInfo::DEBUG_BREAK_SLOT_AT_RETURN);
   mask |= RelocInfo::ModeMask(RelocInfo::DEBUG_BREAK_SLOT_AT_CALL);
   if (type == ALL_BREAK_LOCATIONS) {
     mask |= RelocInfo::ModeMask(RelocInfo::DEBUG_BREAK_SLOT_AT_POSITION);
@@ skipping 60 matching lines @@
 }
 
 BreakLocation::BytecodeArrayIterator::BytecodeArrayIterator(
     Handle<DebugInfo> debug_info, BreakLocatorType type)
     : Iterator(debug_info),
       source_position_iterator_(debug_info->abstract_code()
                                     ->GetBytecodeArray()
                                     ->source_position_table()),
       break_locator_type_(type),
       start_position_(debug_info->shared()->start_position()) {
-  if (!Done()) Next();
+  // There is at least one break location.
+  DCHECK(!Done());
+  Next();
 }
 
 void BreakLocation::BytecodeArrayIterator::Next() {
   DisallowHeapAllocation no_gc;
   DCHECK(!Done());
   bool first = break_index_ == -1;
   while (!Done()) {
     if (!first) source_position_iterator_.Advance();
     first = false;
     if (Done()) return;
@@ skipping 2471 matching lines @@
 }
 
 
 void LockingCommandMessageQueue::Clear() {
   base::LockGuard<base::Mutex> lock_guard(&mutex_);
   queue_.Clear();
 }
 
 }  // namespace internal
 }  // namespace v8