Get rid of PageSet.FromDict from unittests

tools/telemetry/telemetry/value/string_unittest.py

Index: tools/telemetry/telemetry/value/string_unittest.py
diff --git a/tools/telemetry/telemetry/value/string_unittest.py b/tools/telemetry/telemetry/value/string_unittest.py
index 917e55ff9b9c1e4b73f7c6360eb17a3d604eef3e..e50a4dfbc93f1dbb6ef99eb930470099ff5b6921 100644
--- a/tools/telemetry/telemetry/value/string_unittest.py
+++ b/tools/telemetry/telemetry/value/string_unittest.py
@@ -10,15 +10,10 @@ from telemetry.value import string
 
 class TestBase(unittest.TestCase):
   def setUp(self):
-    self.page_set =  page_set.PageSet.FromDict({
-      "description": "hello",
-      "archive_path": "foo.wpr",
-      "pages": [
-        {"url": "http://www.bar.com/"},
-        {"url": "http://www.baz.com/"},
-        {"url": "http://www.foo.com/"}
-        ]
-      }, os.path.dirname(__file__))
+    self.page_set = page_set.PageSet(file_path=os.path.dirname(__file__))
+    self.page_set.AddPageWithDefaultRunNavigate("http://www.bar.com/")
+    self.page_set.AddPageWithDefaultRunNavigate("http://www.baz.com/")
+    self.page_set.AddPageWithDefaultRunNavigate("http://www.foo.com/")
 
   @property
   def pages(self):