Don't remove any entries from the pending deopts table before a throw.

runtime/vm/stack_frame.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_STACK_FRAME_H_
 #define VM_STACK_FRAME_H_
 
 #include "vm/allocation.h"
 #include "vm/object.h"
 #include "vm/stub_code.h"
@@ skipping 105 matching lines @@
     ASSERT(raw_pc != StubCode::DeoptimizeLazyFromThrow_entry()->EntryPoint());
     if (raw_pc == StubCode::DeoptimizeLazyFromReturn_entry()->EntryPoint()) {
       uword fp = GetCallerFp();
       MallocGrowableArray<PendingLazyDeopt>* pending_deopts =
           isolate()->pending_deopts();
       for (intptr_t i = 0; i < pending_deopts->length(); i++) {
         if ((*pending_deopts)[i].fp() == fp) {
           return (*pending_deopts)[i].pc();
         }
       }
-      UNREACHABLE();
+      FATAL("Missing pending deopt entry");
     }
     return raw_pc;
   }
 
   uword fp_;
   uword sp_;
   uword pc_;
   Thread* thread_;
 
   // The iterators FrameSetIterator and StackFrameIterator set the private
@@ skipping 249 matching lines @@
 
 
 DART_FORCE_INLINE static uword LocalVarAddress(uword fp, intptr_t index) {
   return fp + LocalVarIndex(0, index) * kWordSize;
 }
 
 
 }  // namespace dart
 
 #endif  // VM_STACK_FRAME_H_