Take desktop screenshots after test failures in test_runner.py.

ios/build/bots/scripts/test_runner.py

Index: ios/build/bots/scripts/test_runner.py
diff --git a/ios/build/bots/scripts/test_runner.py b/ios/build/bots/scripts/test_runner.py
index 0449975a659e57736ed07c701bab49faf2e297c7..23d612487974feff00c7262ff0c643887d9ed18d 100644
--- a/ios/build/bots/scripts/test_runner.py
+++ b/ios/build/bots/scripts/test_runner.py
@@ -288,6 +288,7 @@ class TestRunner(object):
         stderr=subprocess.STDOUT,
     )
 
+    failure_count = 0
     while True:
       line = proc.stdout.readline()
       if not line:
@@ -297,6 +298,16 @@ class TestRunner(object):
       print line
       sys.stdout.flush()
 
+      # If there is a new test failure, take a desktop screenshot.
+      # parser.FailedTests() considers in progress tests as failed, so a check
+      # is needed that the current test isn't included in the list of failed
+      # tests.
+      new_failure_count = len([test for test in parser.FailedTests()
+                               if test != parser.GetCurrentTest()])
+      if (new_failure_count > failure_count):
+        self.screenshot_desktop()
+        failure_count = new_failure_count
+
     proc.wait()
     sys.stdout.flush()