Fixes crashes in VM isolate shutdown.

runtime/vm/code_generator.cc

 // Copyright (c) 2013, 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.
 
 #include "vm/code_generator.h"
 
 #include "vm/assembler.h"
 #include "vm/ast.h"
 #include "vm/code_patcher.h"
 #include "vm/compiler.h"
@@ skipping 684 matching lines @@
 }
 
 
 // Gets called from debug stub when code reaches a breakpoint
 // set on a runtime stub call.
 DEFINE_RUNTIME_ENTRY(BreakpointRuntimeHandler, 0) {
   ASSERT(isolate->debugger() != NULL);
   DartFrameIterator iterator;
   StackFrame* caller_frame = iterator.NextFrame();
   ASSERT(caller_frame != NULL);
+  ASSERT(isolate->debugger() != NULL);
   uword orig_stub =
       isolate->debugger()->GetPatchedStubAddress(caller_frame->pc());
   isolate->debugger()->SignalBpReached();
   ASSERT((orig_stub & kSmiTagMask) == kSmiTag);
   arguments.SetReturn(Smi::Handle(reinterpret_cast<RawSmi*>(orig_stub)));
 }
 
 
 DEFINE_RUNTIME_ENTRY(SingleStepHandler, 0) {
   ASSERT(isolate->debugger() != NULL);
@@ skipping 327 matching lines @@
       DartEntry::InvokeNoSuchMethod(receiver,
                                     original_function_name,
                                     orig_arguments,
                                     orig_arguments_desc));
   CheckResultError(result);
   arguments.SetReturn(result);
 }
 
 
 static bool CanOptimizeFunction(const Function& function, Isolate* isolate) {
+  ASSERT(isolate->debugger() != NULL);
   const intptr_t kLowInvocationCount = -100000000;
   if (isolate->debugger()->IsStepping() ||
       isolate->debugger()->HasBreakpoint(function)) {
     // We cannot set breakpoints and single step in optimized code,
     // so do not optimize the function.
     function.set_usage_counter(0);
     return false;
   }
   if (function.deoptimization_counter() >=
       FLAG_deoptimization_counter_threshold) {
@@ skipping 107 matching lines @@
       OS::PrintErr("*** Computing stacktrace (%s)\n",
                    function.ToFullyQualifiedCString());
       do_stacktrace = true;
     }
   }
   if (do_deopt) {
     // TODO(turnidge): Consider using DeoptimizeAt instead.
     DeoptimizeFunctionsOnStack();
   }
   if (do_stacktrace) {
+    ASSERT(isolate->debugger() != NULL);
     String& var_name = String::Handle();
     Instance& var_value = Instance::Handle();
     DebuggerStackTrace* stack = isolate->debugger()->StackTrace();
     intptr_t num_frames = stack->Length();
     for (intptr_t i = 0; i < num_frames; i++) {
       ActivationFrame* frame = stack->FrameAt(i);
       // Variable locations and number are unknown when 'always_optimize'.
       const int num_vars =
          Compiler::always_optimize() ? 0 : frame->NumLocalVariables();
       intptr_t unused;
@@ skipping 495 matching lines @@
   const intptr_t elm_size = old_data.ElementSizeInBytes();
   const TypedData& new_data =
       TypedData::Handle(TypedData::New(cid, new_size, Heap::kOld));
   TypedData::Copy(new_data, 0, old_data, 0, old_size * elm_size);
   typed_data_cell.SetAt(0, new_data);
   arguments.SetReturn(new_data);
 }
 
 
 }  // namespace dart