Debugger: preserve stepping state after evaluating breakpoint condition.

src/debug.h

Index: src/debug.h
diff --git a/src/debug.h b/src/debug.h
index 9a9a3ba9239d035b69ed1e6e9c05442cfa0c2259..5fe56d3e212ba3cc43ceba249979d83988c8ce31 100644
--- a/src/debug.h
+++ b/src/debug.h
@@ -732,6 +732,27 @@ class Debug {
     Object** restarter_frame_function_pointer_;
   };
 
+
+  class PreserveDebugState {
+   public:
+    explicit PreserveDebugState(Debug* debug) : debug_(debug) {
+      size_t size = sizeof(debug_->thread_local_);
+      storage_ = NewArray<char>(size);
+      MemCopy(storage_, &debug_->thread_local_, size);
+    }
+
+    ~PreserveDebugState() {
+      size_t size = sizeof(debug_->thread_local_);
+      MemCopy(&debug_->thread_local_, storage_, size);
+      DeleteArray(storage_);
+    }
+
+   private:
+    Debug* debug_;
+    char* storage_;
+  };
+
+
   // Storage location for registers when handling debug break calls
   ThreadLocal thread_local_;