Add an API function to get a debugger stack trace from an error handle.

runtime/vm/dart_api_impl.cc

Index: runtime/vm/dart_api_impl.cc
diff --git a/runtime/vm/dart_api_impl.cc b/runtime/vm/dart_api_impl.cc
index 32fc7bfa6c8ff835d0b6b9b0d5a27cfe12b1aa3f..33be4857eaebbdfa549eefd6adaa96f39a9e0c50 100644
--- a/runtime/vm/dart_api_impl.cc
+++ b/runtime/vm/dart_api_impl.cc
@@ -387,6 +387,70 @@ DART_EXPORT Dart_Handle Dart_ErrorGetStacktrace(Dart_Handle handle) {
   }
 }
 
+DART_EXPORT Dart_Handle Dart_StacktraceLength(Dart_Handle handle,
+                                              intptr_t* length) {
+  Isolate* isolate = Isolate::Current();
+  DARTSCOPE(isolate);
+  const Object& obj = Object::Handle(isolate, Api::UnwrapHandle(handle));
+  if (obj.IsStacktrace()) {
+    const Stacktrace& stacktrace = Stacktrace::Cast(obj);
+    if (length != NULL) {
+      *length = stacktrace.VisibleLength();
+    }
+    return Api::Success();
+  } else {
+    return Api::NewError(
+        "%s expects argument 'handle' to be a stacktrace handle.",
+        CURRENT_FUNC);
+  }
+}
+
+DART_EXPORT Dart_Handle Dart_StacktraceFrameInfo(
+                            Dart_Handle handle,
+                            intptr_t frame_index,
+                            Dart_Handle* function_name,
+                            Dart_Handle* script_url,
+                            intptr_t* line_number,
+                            intptr_t* col_number) {
+  Isolate* isolate = Isolate::Current();
+  DARTSCOPE(isolate);
+  Object& obj = Object::Handle(isolate, Api::UnwrapHandle(handle));
+  if (obj.IsStacktrace()) {
+    const Stacktrace& stacktrace = Stacktrace::Cast(obj);
+    String& internal_function_name = String::Handle();
+    String& internal_script_url = String::Handle();
+    intptr_t internal_line_number = 0;
+    intptr_t internal_col_num = 0;
+    bool in_bounds = stacktrace.VisibleFrameInfoAt(frame_index,
+                                                   &internal_function_name,
+                                                   &internal_script_url,
+                                                   &internal_line_number,
+                                                   &internal_col_num);
+    if (!in_bounds) {
+      return Api::NewError(
+          "%s: frame index was out of bounds (%" Pd ")",
+          CURRENT_FUNC, frame_index);
+    }
+    if (function_name != NULL) {
+      *function_name = Api::NewHandle(isolate, internal_function_name.raw());
+    }
+    if (script_url != NULL) {
+      *script_url = Api::NewHandle(isolate, internal_script_url.raw());
+    }
+    if (line_number != NULL) {
+      *line_number = internal_line_number;
+    }
+    if (col_number != NULL) {
+      *col_number = internal_col_num;
+    }
+    return Api::Success();
+  } else {
+    return Api::NewError(
+        "%s expects argument 'handle' to be a stacktrace handle.",
+        CURRENT_FUNC);
+  }
+}
+
 
 // TODO(turnidge): This clones Api::NewError.  I need to use va_copy to
 // fix this but not sure if it available on all of our builds.