Remove unnecessary isolate argument from some visitors

runtime/vm/profiler.cc

Index: runtime/vm/profiler.cc
diff --git a/runtime/vm/profiler.cc b/runtime/vm/profiler.cc
index 37b8b73577f7f5426867ceb40c0681440b4a0198..e597260ef88b15c17687e3eff6636eebd15e189c 100644
--- a/runtime/vm/profiler.cc
+++ b/runtime/vm/profiler.cc
@@ -1125,9 +1125,7 @@ CodeLookupTable::CodeLookupTable(Thread* thread) {
 
 class CodeLookupTableBuilder : public ObjectVisitor {
  public:
-  CodeLookupTableBuilder(Isolate* isolate, CodeLookupTable* table)
-      : ObjectVisitor(isolate),
-        table_(table) {
+  explicit CodeLookupTableBuilder(CodeLookupTable* table) : table_(table) {
     ASSERT(table_ != NULL);
   }
 
@@ -1163,7 +1161,7 @@ void CodeLookupTable::Build(Thread* thread) {
   code_objects_.Clear();
 
   // Add all found Code objects.
-  CodeLookupTableBuilder cltb(isolate, this);
+  CodeLookupTableBuilder cltb(this);
   vm_isolate->heap()->IterateOldObjects(&cltb);
   isolate->heap()->IterateOldObjects(&cltb);