Fix several little buglets with stepping

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 1874 matching lines @@
   // interested in.
   ActivationFrame* frame = TopDartFrame();
   ASSERT(frame != NULL);
   const Function& func = frame->function();
   if (!IsDebuggable(func)) {
     return;
   }
   if (frame->TokenPos() == Scanner::kDummyTokenIndex) {
     return;
   }
+  // Don't pause for a single step if there is a breakpoint set
+  // at this location.
+  if (HasActiveBreakpoint(frame->pc())) {
+    return;
+  }
 
   if (FLAG_verbose_debug) {
     OS::Print(">>> single step break at %s:%" Pd " (func %s token %" Pd ")\n",
               String::Handle(frame->SourceUrl()).ToCString(),
               frame->LineNumber(),
               String::Handle(frame->QualifiedFunctionName()).ToCString(),
               frame->TokenPos());
   }
 
   ASSERT(stack_trace_ == NULL);
@@ skipping 189 matching lines @@
                   bpt->LineNumber(),
                   func.IsClosureFunction() ? "closure" : "function",
                   String::Handle(func.name()).ToCString());
       }
       MakeCodeBreakpointsAt(func, bpt);
     }
   }
 }
 
 
+// TODO(hausner): Could potentially make this faster by checking
+// whether the call target at pc is a debugger stub.
+bool Debugger::HasActiveBreakpoint(uword pc) {
+  CodeBreakpoint* bpt = GetCodeBreakpoint(pc);
+  return (bpt != NULL) && (bpt->IsEnabled());
+}
+
+
 CodeBreakpoint* Debugger::GetCodeBreakpoint(uword breakpoint_address) {
   CodeBreakpoint* bpt = code_breakpoints_;
   while (bpt != NULL) {
     if (bpt->pc() == breakpoint_address) {
       return bpt;
     }
     bpt = bpt->next();
   }
   return NULL;
 }
@@ skipping 108 matching lines @@
 }
 
 
 void Debugger::RegisterCodeBreakpoint(CodeBreakpoint* bpt) {
   ASSERT(bpt->next() == NULL);
   bpt->set_next(code_breakpoints_);
   code_breakpoints_ = bpt;
 }
 
 }  // namespace dart