Remove an invalid assert in converting a dart.core.Stacktrace to a debugger stacktrace.

runtime/vm/debugger.cc

 // Copyright (c) 2012, 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/debugger.h"
 
 #include "include/dart_api.h"
 
 #include "vm/code_generator.h"
 #include "vm/code_patcher.h"
@@ skipping 1282 matching lines @@
   Function& function = Function::Handle();
   Code& code = Code::Handle();
 
   const uword fp = 0;
   const uword sp = 0;
   const Array& deopt_frame = Array::Handle();
   const intptr_t deopt_frame_offset = -1;
 
   for (intptr_t i = 0; i < ex_trace.Length(); i++) {
     function = ex_trace.FunctionAtFrame(i);
-    if (function.IsNull()) {
-      // Check if null function object indicates a stack trace overflow.
-      // Preallocated stacktraces like StackOverflow or OutOfMemory make skip
-      // frames.
-      ASSERT((i < (ex_trace.Length() - 1)) &&
-          (ex_trace.FunctionAtFrame(i + 1) != Function::null()));
-    } else if (function.is_visible()) {
+    // Pre-allocated Stacktraces may include empty slots, either (a) to indicate
+    // where frames were omitted in the case a stack has more frames than the
+    // pre-allocated trace (such as a stack overflow) or (b) because a stack has
+    // fewer frames that the pre-allocated trace (such as memory exhaustion with
+    // a shallow stack).
+    if (!function.IsNull() && function.is_visible()) {
       code = ex_trace.CodeAtFrame(i);
       ASSERT(function.raw() == code.function());
       uword pc = code.EntryPoint() + Smi::Value(ex_trace.PcOffsetAtFrame(i));
       if (code.is_optimized() && ex_trace.expand_inlined()) {
         // Traverse inlined frames.
         for (InlinedFunctionsIterator it(code, pc); !it.Done(); it.Advance()) {
           function = it.function();
           code = it.code();
           ASSERT(function.raw() == code.function());
           uword pc = it.pc();
@@ skipping 907 matching lines @@
 }
 
 
 void Debugger::RegisterCodeBreakpoint(CodeBreakpoint* bpt) {
   ASSERT(bpt->next() == NULL);
   bpt->set_next(code_breakpoints_);
   code_breakpoints_ = bpt;
 }
 
 }  // namespace dart