[debugger] remove some dead code.

src/debug/debug.cc

Index: src/debug/debug.cc
diff --git a/src/debug/debug.cc b/src/debug/debug.cc
index 094fd609c346c83029af89efcd7d06dac75883cc..2aac6aa117d54f1e5908170dea5ae20f2fc1dd9d 100644
--- a/src/debug/debug.cc
+++ b/src/debug/debug.cc
@@ -300,10 +300,9 @@ void BreakLocation::ClearDebugBreak() {
 
 
 bool BreakLocation::IsDebugBreak() const {
-  if (IsDebugBreakSlot()) {
-    return rinfo().IsPatchedDebugBreakSlotSequence();
-  }
-  return false;
+  if (IsDebuggerStatement()) return false;
+  DCHECK(IsDebugBreakSlot());
+  return rinfo().IsPatchedDebugBreakSlotSequence();
 }
 
 
@@ -987,14 +986,6 @@ bool Debug::StepNextContinue(BreakLocation* break_location,
 }
 
 
-// Check whether the code object at the specified address is a debug break code
-// object.
-bool Debug::IsDebugBreak(Address addr) {
-  Code* code = Code::GetCodeFromTargetAddress(addr);
-  return code->is_debug_stub();
-}
-
-
 // Simple function for returning the source positions for active break points.
 Handle<Object> Debug::GetSourceBreakLocations(
     Handle<SharedFunctionInfo> shared,