Make exception thrown via v8 public API propagate to v8::TryCatch as JS thrown exceptions do.

src/top.h

Index: src/top.h
diff --git a/src/top.h b/src/top.h
index 26ae542f59b72d0a6e01149dab757cafb4a53574..0dbc3094fa95f7bd29ff6c7b353ad90dc79d09a7 100644
--- a/src/top.h
+++ b/src/top.h
@@ -195,22 +195,26 @@ class Top {
     ASSERT(has_pending_exception());
     return thread_local_.pending_exception_;
   }
-  static bool external_caught_exception() {
-    return thread_local_.external_caught_exception_;
-  }
   static void set_pending_exception(MaybeObject* exception) {
     thread_local_.pending_exception_ = exception;
   }
   static void clear_pending_exception() {
     thread_local_.pending_exception_ = Heap::the_hole_value();
   }
-
   static MaybeObject** pending_exception_address() {
     return &thread_local_.pending_exception_;
   }
   static bool has_pending_exception() {
     return !thread_local_.pending_exception_->IsTheHole();
   }
+
+  static bool external_caught_exception() {
+    return thread_local_.external_caught_exception_;
+  }
+  static void set_external_caught_exception(bool value) {
+    thread_local_.external_caught_exception_ = value;
+  }
+
   static void clear_pending_message() {
     thread_local_.has_pending_message_ = false;
     thread_local_.pending_message_ = NULL;
@@ -461,6 +465,18 @@ class Top {
   static const char* kStackOverflowMessage;
 
  private:
+
+  static v8::TryCatch* catcher() {
+    return thread_local_.catcher_;
+  }
+
+  static void set_catcher(v8::TryCatch* catcher) {
+    thread_local_.catcher_ = catcher;
+  }
+
+  // Attempts to propagate the pending exception to the proper v8::TryCatch.
+  static void PropagatePendingExceptionToExternalTryCatch();
+
 #ifdef ENABLE_VMSTATE_TRACKING
   // Set of states used when communicating with the runtime profiler.
   //
@@ -525,6 +541,26 @@ class Top {
   friend class ThreadLocalTop;
 
   static void FillCache();
+
+ public:
+  class ExceptionScope {
+   public:
+    ExceptionScope() :
+      // Scope currently can only be used for regular exceptions, not
+      // failures like OOM or termination exception.
+      pending_exception_(Top::pending_exception()->ToObjectUnchecked()),
+      catcher_(Top::catcher())
+    { }
+
+    ~ExceptionScope() {
+      Top::set_catcher(catcher_);
+      Top::set_pending_exception(*pending_exception_);
+    }
+
+   private:
+    Handle<Object> pending_exception_;
+    v8::TryCatch* catcher_;
+  };
 };