Add a line number filter for layout tests. Suppress/fix Dartium layout tests.

Tools/Scripts/webkitpy/layout_tests/controllers/single_test_runner.py

Index: Tools/Scripts/webkitpy/layout_tests/controllers/single_test_runner.py
diff --git a/Tools/Scripts/webkitpy/layout_tests/controllers/single_test_runner.py b/Tools/Scripts/webkitpy/layout_tests/controllers/single_test_runner.py
index 0a7483069b96b5f3568cb78f0a41e03129b089d9..1dfe1c4bfe6329abf81e0badd70d69f08e2385f6 100644
--- a/Tools/Scripts/webkitpy/layout_tests/controllers/single_test_runner.py
+++ b/Tools/Scripts/webkitpy/layout_tests/controllers/single_test_runner.py
@@ -311,6 +311,10 @@ class SingleTestRunner(object):
 
     _observatory_cleaner = re.compile(r"^Observatory.*\n", re.MULTILINE)
     _console_observatory_cleaner = re.compile(r"^CONSOLE INFO: Observatory.*\n", re.MULTILINE)
+    _line_number_cleaner = re.compile(r"\(dart:(\w+):\d+\)", re.MULTILINE)
+
+    def _line_number_substitution(self, match):
+        return "(dart:" + match.group(1) + ":xxxx)"
 
     def _get_normalized_output_text(self, output):
         """Returns the normalized text output, i.e. the output in which
@@ -322,6 +326,7 @@ class SingleTestRunner(object):
         normalized_lines = output.replace("\r\r\n", "\r\n").replace("\r\n", "\n")
         normalized_lines = re.sub(self._observatory_cleaner, r"", normalized_lines)
         normalized_lines = re.sub(self._console_observatory_cleaner, r"", normalized_lines)
+        normalized_lines = re.sub(self._line_number_cleaner, self._line_number_substitution, normalized_lines)
         return normalized_lines
 
     # FIXME: This function also creates the image diff. Maybe that work should