stackdriver: get default project from backend. also ensure default project could be retrieved when authentication type is gce

pkg/tsdb/stackdriver/default_project_query.go

@@ -0,0 +1,22 @@
+package stackdriver
+
+import (
+	"context"
+
+	"github.com/grafana/grafana/pkg/components/simplejson"
+	"github.com/grafana/grafana/pkg/tsdb"
+)
+
+func (e *StackdriverExecutor) getGceDefaultProject(ctx context.Context, tsdbQuery *tsdb.TsdbQuery) (*tsdb.Response, error) {
+	queryResult := &tsdb.QueryResult{Meta: simplejson.New(), RefId: tsdbQuery.Queries[0].RefId}
+	result := &tsdb.Response{
+		Results: make(map[string]*tsdb.QueryResult),
+	}
+	defaultProject, err := e.getDefaultProject(ctx)
+	if err != nil {
+		return nil, err
+	}
+	queryResult.Meta.Set("defaultProject", defaultProject)
+	result.Results[tsdbQuery.Queries[0].RefId] = queryResult
+	return result, nil
+}