fix PathObserver to avoid try+catch

pkg/pkg.status

 # 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.
 
 # Don't run any test-like files that show up in packages directories. It
 # shouldn't be necessary to run "pub install" in these packages, but if you do
 # it shouldn't break the tests.
 */packages/*/*: Skip
 */*/packages/*/*: Skip
 */*/*/packages/*/*: Skip
@@ skipping 290 matching lines @@
 intl/test/message_extraction/message_extraction_test: Pass, Fail # Issue 12930
 
 [ $compiler == none && ($runtime == dartium || $runtime == drt) ]
 source_maps/test/parser_test: Pass, Timeout # Issue 13719: Please triage this failure.
 polymer_expressions/test/bindings_test: Fail, Pass # Issue 14445.
 
 [ $compiler == dartanalyzer ]
 # pkg issue 13944; Missing inherited member 'Observable._mirror'
 custom_element/test/analyzer_test: fail
 template_binding/test/analyzer_test: fail
-observe/test/observe_test: fail
 
 [ $compiler == dart2analyzer ]
 # pkg issue 13944; Missing inherited members: 'ListChangeRecord.addedCount' and 'ListChangeRecord.removedCount'
 custom_element/test/analyzer_test: fail
 template_binding/test/analyzer_test: fail
-observe/test/observe_test: fail
-
-# pkg issue 13945; Missing inherited member 'Trace.frames'
-observe/test/observe_test: fail
 
 [ $compiler == dartanalyzer || $compiler == dart2analyzer ]
 barback/test/asset_id_test: StaticWarning
 barback/test/asset_set_test: StaticWarning
 barback/test/asset_test: StaticWarning
 barback/test/cancelable_future_test: StaticWarning
 barback/test/mutliset_test: StaticWarning
 barback/test/package_graph/add_remove_transform_test: StaticWarning
 barback/test/package_graph/errors_test: StaticWarning
 barback/test/package_graph/get_all_assets_test: StaticWarning
@@ skipping 25 matching lines @@
 http/test/http_test: StaticWarning
 http/test/mock_client_test: StaticWarning
 http/test/multipart_test: StaticWarning
 http/test/request_test: StaticWarning
 http/test/streamed_request_test: StaticWarning
 intl/test/date_time_format_file_even_test: StaticWarning
 intl/test/date_time_format_file_odd_test: StaticWarning
 intl/test/date_time_format_http_request_test: StaticWarning
 intl/test/date_time_format_local_even_test: StaticWarning
 intl/test/date_time_format_local_odd_test: StaticWarning
-observe/test/list_change_test: StaticWarning
-observe/test/observable_list_test: StaticWarning
-observe/test/observable_map_test: StaticWarning
-observe/test/path_observer_test: StaticWarning
-observe/test/transform_test: CompileTimeError, StaticWarning
+observe/test/transform_test: StaticWarning
 polymer/example/component/news/test/news_index_test: StaticWarning
 polymer_expressions/test/bindings_test: StaticWarning
 polymer_expressions/test/eval_test: StaticWarning
 polymer_expressions/test/globals_test: StaticWarning
 polymer_expressions/test/syntax_test: StaticWarning
 polymer/test/attr_deserialize_test: StaticWarning
 polymer/test/attr_mustache_test: StaticWarning
 polymer/test/bind_mdv_test: StaticWarning
 polymer/test/bind_test: StaticWarning
 polymer/test/build/all_phases_test: CompileTimeError, StaticWarning
@@ skipping 42 matching lines @@
 template_binding/test/binding_syntax_test: StaticWarning
 template_binding/test/custom_element_bindings_test: StaticWarning
 template_binding/test/element_bindings_test: StaticWarning
 template_binding/test/node_bindings_test: StaticWarning
 template_binding/test/template_element_test: StaticWarning
 unittest/test/matchers_test: StaticWarning
 unittest/test/mock_test: StaticWarning
 watcher/test/directory_watcher_test: StaticWarning
 watcher/test/no_subscription_test: StaticWarning
 watcher/test/ready_test: StaticWarning