Integrate wptrunner screenshots into results viewer.

The wptrunner output file contains a "screenshots" artifact which is a
list of files that were screenshotted, and the base64-encoded png of the
screenshot that was taken. We extract and decode these pngs and write
them to disk. The redundant data is then scrubbed from the output file
and replaced with the path to the newly-created file.

Bug: 937369
Change-Id: Ifeff993023219833e65af39548f556b54ac65b60
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2252682
Commit-Queue: Luke Z <lpz@chromium.org>
Reviewed-by: Rakib Hasan <rmhasan@google.com>
Reviewed-by: Robert Ma <robertma@chromium.org>
Cr-Commit-Position: refs/heads/master@{#780415}

testing/scripts/wpt_common.py

@@ -2,6 +2,7 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+import base64
 import json
 import os
 import shutil
@@ -16,6 +17,7 @@ if BLINK_TOOLS_DIR not in sys.path:
     sys.path.append(BLINK_TOOLS_DIR)
 
 from blinkpy.common.host import Host
+from blinkpy.web_tests.models import test_failures
 
 class BaseWptScriptAdapter(common.BaseIsolatedScriptArgsAdapter):
     """The base class for script adapters that use wptrunner to execute web
@@ -102,18 +104,25 @@ class BaseWptScriptAdapter(common.BaseIsolatedScriptArgsAdapter):
                     results_dir, path_so_far, log_artifact)
                 root_node["artifacts"]["actual_text"] = [artifact_subpath]
 
-            # TODO(lpz): For now we just discard the screenshot artifact to keep
-            # the output file size small. Writing screenshots to disk will be
-            # added in a follow-up.
             screenshot_artifact = root_node["artifacts"].pop("screenshots",
                                                              None)
+            if screenshot_artifact:
+                screenshot_paths_dict = self._write_screenshot_artifact(
+                    results_dir, path_so_far, screenshot_artifact)
+                for screenshot_key, path in screenshot_paths_dict.items():
+                    root_node["artifacts"][screenshot_key] = [path]
 
             # Fixup statuses so the results viewer understands them. We have to
             # use the deprecated statuses instead of "FAIL".
             if root_node["actual"] == "FAIL":
-                if screenshot_artifact:
+                if log_artifact and screenshot_artifact:
+                    root_node["actual"] = "IMAGE+TEXT"
+                elif screenshot_artifact:
                     root_node["actual"] = "IMAGE"
                 else:
+                    # Fallback to text even if there are no artifacts, because
+                    # the results viewer will not display a test at all if its
+                    # status remains "FAIL".
                     root_node["actual"] = "TEXT"
             return
 
@@ -145,7 +154,8 @@ class BaseWptScriptAdapter(common.BaseIsolatedScriptArgsAdapter):
         log_artifact_sub_path = (
             os.path.join("layout-test-results",
                          self.port.output_filename(
-                             test_name, "-actual", ".txt"))
+                             test_name, test_failures.FILENAME_SUFFIX_ACTUAL,
+                             ".txt"))
         )
         log_artifact_full_path = os.path.join(results_dir,
                                               log_artifact_sub_path)
@@ -155,3 +165,53 @@ class BaseWptScriptAdapter(common.BaseIsolatedScriptArgsAdapter):
             artifact_file.write("\n".join(log_artifact).encode("utf-8"))
 
         return log_artifact_sub_path
+
+    def _write_screenshot_artifact(self, results_dir, test_name,
+                                   screenshot_artifact):
+        """Write screenshot artifact to disk.
+
+        The screenshot artifact is a list of strings, each of which has the
+        format <url>:<base64-encoded PNG>. Each url-png pair is a screenshot of
+        either the test, or one of its refs. We can identify which screenshot is
+        for the test by comparing the url piece to the test name.
+
+        Args:
+           results_dir: str path to the directory that results live in
+           test:name str name of the test that this artifact is for
+           screenshot_artifact: list of strings, each being a url-png pair as
+               described above.
+
+        Returns:
+             A dict mapping the screenshot key (ie: actual, expected) to the
+             path of the file for that screenshot
+        """
+        result={}
+        for screenshot_pair in screenshot_artifact:
+            screenshot_split = screenshot_pair.split(":")
+            url = screenshot_split[0]
+            # The url produced by wptrunner will have a leading / which we trim
+            # away for easier comparison to the test_name below.
+            if url.startswith("/"):
+                url = url[1:]
+            image_bytes = base64.b64decode(screenshot_split[1].strip())
+
+            screenshot_key = "expected_image"
+            file_suffix = test_failures.FILENAME_SUFFIX_EXPECTED
+            if test_name == url:
+                screenshot_key = "actual_image"
+                file_suffix = test_failures.FILENAME_SUFFIX_ACTUAL
+
+            screenshot_sub_path = (
+                os.path.join("layout-test-results",
+                             self.port.output_filename(
+                                 test_name, file_suffix, ".png"))
+            )
+            result[screenshot_key] = screenshot_sub_path
+
+            screenshot_full_path = os.path.join(results_dir,screenshot_sub_path)
+            if not os.path.exists(os.path.dirname(screenshot_full_path)):
+                os.makedirs(os.path.dirname(screenshot_full_path))
+            # Note: we are writing raw bytes to this file
+            with open(screenshot_full_path, "wb") as artifact_file:
+                artifact_file.write(image_bytes)
+        return result