If an unhandled exception occurs in Dart_RunLoop, pass it out to the caller.

runtime/vm/isolate.h

 // Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #ifndef VM_ISOLATE_H_
 #define VM_ISOLATE_H_
 
 #include <limits.h>
 
 #include "include/dart_api.h"
 #include "vm/assert.h"
 #include "vm/store_buffer.h"
 #include "vm/timer.h"
 
 namespace dart {
 
 // Forward declarations.
 class ApiState;
 class BigintStore;
 class CodeIndexTable;
 class Debugger;
 class HandleScope;
 class Heap;
 class LongJump;
 class MessageQueue;
 class Monitor;
 class ObjectPointerVisitor;
 class ObjectStore;
 class RawContext;
+class RawObject;
 class StackResource;
 class StubCode;
 class Zone;
 
 class Isolate {
  public:
   ~Isolate();
 
   static inline Isolate* Current();
   static void SetCurrent(Isolate* isolate);
@@ skipping 183 matching lines @@
 
   uword stack_limit_address() const {
     return reinterpret_cast<uword>(&stack_limit_);
   }
 
   void SetStackLimit(uword value);
   uword stack_limit() const { return stack_limit_; }
 
   void SetStackLimitFromCurrentTOS(uword isolate_stack_top);
 
-  void StandardRunLoop();
+  // Returns null on success, unhandled exception on failure.
+  RawObject* StandardRunLoop();
 
   intptr_t ast_node_id() const { return ast_node_id_; }
   void set_ast_node_id(int value) { ast_node_id_ = value; }
 
   Debugger* debugger() const { return debugger_; }
 
  private:
   Isolate();
 
   void PrintInvokedFunctions();
@@ skipping 46 matching lines @@
 #include "vm/isolate_linux.h"
 #elif defined(TARGET_OS_MACOS)
 #include "vm/isolate_macos.h"
 #elif defined(TARGET_OS_WINDOWS)
 #include "vm/isolate_win.h"
 #else
 #error Unknown target os.
 #endif
 
 #endif  // VM_ISOLATE_H_