--- a/testing/web-platform/tests/tools/wptrunner/wptrunner/metadata.py
+++ b/testing/web-platform/tests/tools/wptrunner/wptrunner/metadata.py
@@ -230,23 +230,58 @@ class ExpectedUpdater(object):
         for manifest in test_manifests.iterkeys():
             for test_type, path, _ in manifest:
                 if test_type in wpttest.manifest_test_cls:
                     self.types_by_path[path] = wpttest.manifest_test_cls[test_type]
         self.run_infos = []
 
     def update_from_log(self, log_file):
         self.run_info = None
+        try:
+            data = json.load(log_file)
+        except Exception:
+            pass
+        else:
+            if "action" not in data and "results" in data:
+                self.update_from_wptreport_log(data)
+                return
+
+        log_file.seek(0)
+        self.update_from_raw_log(log_file)
+
+    def update_from_raw_log(self, log_file):
         action_map = self.action_map
         for line in log_file:
             data = json.loads(line)
             action = data["action"]
             if action in action_map:
                 action_map[action](data)
 
+    def update_from_wptreport_log(self, data):
+        action_map = self.action_map
+        action_map["suite_start"]({"run_info": data["run_info"]})
+        for test in data["results"]:
+            action_map["test_start"]({"test": test["test"]})
+            for subtest in test["subtests"]:
+                action_map["test_status"]({"test": test["test"],
+                                           "subtest": subtest["name"],
+                                           "status": subtest["status"],
+                                           "expected": subtest.get("expected")})
+            action_map["test_end"]({"test": test["test"],
+                                    "status": test["status"],
+                                    "expected": test.get("expected")})
+            if "asserts" in test:
+                asserts = test["asserts"]
+                action_map["assertion_count"]({"test": test["test"],
+                                               "count": asserts["count"],
+                                               "min_expected": asserts["min"],
+                                               "max_expected": asserts["max"]})
+        for item in data.get("lsan_leaks", []):
+            action_map["lsan_leak"](item)
+
     def suite_start(self, data):
         self.run_info = data["run_info"]
 
     def test_start(self, data):
         test_id = data["test"]
         try:
             test_data = self.id_test_map[test_id]
         except KeyError:

--- a/testing/web-platform/tests/tools/wptrunner/wptrunner/tests/test_update.py
+++ b/testing/web-platform/tests/tools/wptrunner/wptrunner/tests/test_update.py
@@ -1,8 +1,9 @@
+import json
 import mock
 import os
 import sys
 from io import BytesIO
 
 from .. import metadata, manifestupdate, wptmanifest
 from mozlog import structuredlog, handlers, formatters
 
@@ -66,25 +67,28 @@ def create_updater(tests, url_base="/", 
                                                      url_base)
         for test_id in test_ids:
             id_test_map[test_id] = test_data
 
     return id_test_map, metadata.ExpectedUpdater(test_manifests, id_test_map, **kwargs)
 
 
 def create_log(entries):
-    logger = structuredlog.StructuredLogger("expected_test")
     data = BytesIO()
-    handler = handlers.StreamHandler(data, formatters.JSONFormatter())
-    logger.add_handler(handler)
+    if isinstance(entries, list):
+        logger = structuredlog.StructuredLogger("expected_test")
+        handler = handlers.StreamHandler(data, formatters.JSONFormatter())
+        logger.add_handler(handler)
 
-    for item in entries:
-        action, kwargs = item
-        getattr(logger, action)(**kwargs)
-    logger.remove_handler(handler)
+        for item in entries:
+            action, kwargs = item
+            getattr(logger, action)(**kwargs)
+        logger.remove_handler(handler)
+    else:
+        json.dump(entries, data)
     data.seek(0)
     return data
 
 
 def suite_log(entries, run_info=None):
     return ([("suite_start", {"tests": [], "run_info": run_info or {}})] +
             entries +
             [("suite_end", {})])
@@ -563,8 +567,43 @@ def test_update_lsan_3():
                       run_info={"os": "linux"})
 
 
     updated = update(tests, log_0, log_1)
     new_manifest = updated[0][1]
 
     assert not new_manifest.is_empty
     assert new_manifest.get("lsan-allowed") == ["baz", "foo"]
+
+
+def test_update_wptreport_0():
+    tests = [("path/to/test.htm", ["/path/to/test.htm"], "testharness",
+              """[test.htm]
+  [test1]
+    expected: FAIL""")]
+
+    log = {"run_info": {},
+           "results": [
+               {"test": "/path/to/test.htm",
+                "subtests": [{"name": "test1",
+                              "status": "PASS",
+                              "expected": "FAIL"}],
+                "status": "OK"}
+           ]}
+
+    updated = update(tests, log)
+
+    assert len(updated) == 1
+    assert updated[0][1].is_empty
+
+
+def test_update_wptreport_1():
+    tests = [("path/to/__dir__", ["path/to/__dir__"], None, "")]
+
+    log = {"run_info": {},
+           "results": [],
+           "lsan_leaks": [{"scope": "path/to/",
+                           "frames": ["baz", "foobar"]}]}
+
+    updated = update(tests, log)
+
+    assert len(updated) == 1
+    assert updated[0][1].get("lsan-allowed") == ["baz"]