Avoid allocating an exception object in the snapshot reader.

runtime/vm/snapshot.cc

Index: runtime/vm/snapshot.cc
===================================================================
--- runtime/vm/snapshot.cc	(revision 38187)
+++ runtime/vm/snapshot.cc	(working copy)
@@ -167,8 +167,6 @@
 
 
 RawObject* SnapshotReader::ReadObject() {
-  const Instance& null_object = Instance::Handle();
-  *ErrorHandle() = UnhandledException::New(null_object, null_object);
   // Setup for long jump in case there is an exception while reading.
   LongJumpScope jump;
   if (setjmp(*jump.Set()) == 0) {
@@ -724,6 +722,8 @@
     // into dart code or allocating any code.
     // We do a longjmp at this point to unwind out of the entire
     // read part and return the error object back.
+    const Instance& null_object = Instance::Handle();
+    *ErrorHandle() = UnhandledException::New(null_object, null_object);

[siva, 2014/07/14 16:20:03]

TryAllocate just failed which means the heap is full, how will
UnhandledException::New(...) succeed?

Maybe we should preallocate the UnhandledException object just like how we
preallocate the out_of_memory exception object.

[Florian Schneider, 2014/07/14 17:02:40]

Good point. I'll try that instead.

     const Instance& exception =
         Instance::Handle(object_store()->out_of_memory());
     ErrorHandle()->set_exception(exception);