Add about:crash to known crashes.

chrome/test/data/reliability/known_crashes.txt

 # This file contains known patterns of crash signatures. One pattern per line.
 #
 # A crash signature is the concatenation of the top N functions, delimited by
 # '___', in chrome.dll on the crash stack. All characters are lower case.
 #
 # We use crash signature patterns as our list of known crashes. A crash
 # signature pattern is a string that can be used to identify a known crash. We
 # use the notion of patterns because crashes with the same root cause can often
 # differ somewhat in their crash stacks. A pattern is intended to be a
 # generalized, yet still identifying, form of a particular crash. Usually a
 # pattern will contain part of a crash signature, for example a prefix, but it
 # can be more sophisticated, such as a regular expression. See below for more
 # details.
 #
 # The format of known crashes in this file is as follows:
 #   TYPE : PATTERN
 #
 # PATTERN: A crash signature pattern is a potentially identifying string that
 #          can be used to match a crash signature.
 # TYPE: The type of the pattern, indicates how the pattern should be matched
 #       against crash signatures. Possible options are:
 #           PREFIX: Match any signature beginning with this pattern.
 #           SUBSTRING: Match any signature containing this pattern.
 #           REGEX: Use this pattern as a regex to match against signatures.
 #       If the type is not listed, it defaults to PREFIX.
 
+# about:crash is a test page.
+PREFIX : abouthandler::aboutcrash
+
 # Any crash due to out of memory is ignored.
 PREFIX : `anonymous namespace'::onnomemory
 
 # Mysterious crashes. Leave them for now.
 
 # It is too broad to exclude all purecall related crashes. Thus here we filter
 # any purecall crash immediately after runtask.
 SUBSTRING : purecall___messageloop::runtask
 REGEX : purecall___[^_]*___messageloop::runtask
 REGEX : `anonymous namespace'::purecall$
@@ skipping 97 matching lines @@
 SUBSTRING : webframeloaderclient::dispatchdidchangelocationwithinpage___webcore::frameloader::continuefragmentscrollafternavigationpolicy___webcore::frameloader::callcontinuefragmentscrollafternavigationpolicy___webcore::policycheck::call
 
 # 23281
 REGEX : tabcontents::washidden___.*___tabcontents::~tabcontents
 
 # bug 23780
 PREFIX : v8::internal::mayaccessprecheck
 
 # bug 25689
 PREFIX : skia::crashforbitmapallocationfailure___skia::platformcanvas::platformcanvas___webpluginproxy::setwindowlessbuffer___webpluginproxy::updategeometry___webplugindelegatestub