Add suppression to test.dart for flaky content_shell crashes

tools/testing/dart/status_file_parser.dart

Index: tools/testing/dart/status_file_parser.dart
diff --git a/tools/testing/dart/status_file_parser.dart b/tools/testing/dart/status_file_parser.dart
index 8fa9bb7dda2ddc3016ecf04d04fee1d2667d3b5d..c4be8017191523a5e3afe638929c6032ac23ac35 100644
--- a/tools/testing/dart/status_file_parser.dart
+++ b/tools/testing/dart/status_file_parser.dart
@@ -35,6 +35,11 @@ class Expectation {
   static Expectation SKIP_SLOW = byName('SkipSlow');
   static Expectation SKIP_BY_DESIGN = byName('SkipByDesign');
 
+  // Can be returned by the test runner to say the result should be ignored,
+  // and assumed to meet the expectations, due to an infrastructure failure.
+  // Do not place in status files.

[kustermann, 2016/06/21 14:22:19]

Maybe *ensure* this in the status file parser?

[Bill Hesse, 2016/06/24 12:06:59]

Not easy to do.  Perhaps other statuses should also be forbidden.

+  static Expectation IGNORE = byName('Ignore');
+
   static Expectation byName(String name) {
     _initialize();
     name = name.toLowerCase();
@@ -77,6 +82,7 @@ class Expectation {
       build("SkipSlow", group: skip, isMetaExpectation: true);
       build("Ok", isMetaExpectation: true);
       build("Slow", isMetaExpectation: true);
+      build("Ignore");
     }
   }
 
@@ -94,6 +100,7 @@ class Expectation {
 
   bool canBeOutcomeOf(Expectation expectation) {
     Expectation outcome = this;
+    if (outcome == IGNORE) return true;

[kustermann, 2016/06/21 14:22:19]

This is the controversial line: If you submit this change, then the bot can
suddenly have an issue with the X display and *nonetheless*:

  * build bot will be absolutely green
  * status files will be absolutely empty
  * everybody will be absolutely happy

Even if *none* of the tests are run anymore.

=> So I'm not really a fan of this.

[Bill Hesse, 2016/06/24 12:06:59]

I have added code to monitor the number of tests that are skipped this way, and
if more than 5 are, the test suite will fail.

Done.

     while (outcome != null) {
       if (outcome == expectation) {
         return true;