Cache isolate in the StackTrace object to that we don't call

runtime/vm/handles.cc

Index: runtime/vm/handles.cc
===================================================================
--- runtime/vm/handles.cc	(revision 1423)
+++ runtime/vm/handles.cc	(working copy)
@@ -70,45 +70,41 @@
 
 
 HandleScope::HandleScope() : StackResource() {
-  Isolate* isolate = Isolate::Current();
-  ASSERT(isolate->no_handle_scope_depth() == 0);
-  VMHandles* handles = isolate->current_zone()->handles();
+  ASSERT(isolate()->no_handle_scope_depth() == 0);
+  VMHandles* handles = isolate()->current_zone()->handles();
   ASSERT(handles != NULL);
   saved_handle_block_ = handles->scoped_blocks_;
   saved_handle_slot_ = handles->scoped_blocks_->next_handle_slot();
 #if defined(DEBUG)
-  link_ = isolate->top_handle_scope();
-  isolate->set_top_handle_scope(this);
+  link_ = isolate()->top_handle_scope();
+  isolate()->set_top_handle_scope(this);
 #endif
 }
 
 
 HandleScope::~HandleScope() {
-  Isolate* isolate = Isolate::Current();
-  ASSERT(isolate->current_zone() != NULL);
-  VMHandles* handles = isolate->current_zone()->handles();
+  ASSERT(isolate()->current_zone() != NULL);
+  VMHandles* handles = isolate()->current_zone()->handles();
   ASSERT(handles != NULL);
   handles->scoped_blocks_ = saved_handle_block_;
   handles->scoped_blocks_->set_next_handle_slot(saved_handle_slot_);
 #if defined(DEBUG)
   handles->VerifyScopedHandleState();
   handles->ZapFreeScopedHandles();
-  ASSERT(isolate->top_handle_scope() == this);
-  isolate->set_top_handle_scope(link_);
+  ASSERT(isolate()->top_handle_scope() == this);
+  isolate()->set_top_handle_scope(link_);
 #endif
 }
 
 
 #if defined(DEBUG)
 NoHandleScope::NoHandleScope() : StackResource() {
-  Isolate* isolate = Isolate::Current();
-  isolate->IncrementNoHandleScopeDepth();
+  isolate()->IncrementNoHandleScopeDepth();
 }
 
 
 NoHandleScope::~NoHandleScope() {
-  Isolate* isolate = Isolate::Current();
-  isolate->DecrementNoHandleScopeDepth();
+  isolate()->DecrementNoHandleScopeDepth();
 }
 #endif  // defined(DEBUG)