Change the default --retry-limit for telemetry*unittests.

tools/telemetry/telemetry/unittest/run_tests.py

Index: tools/telemetry/telemetry/unittest/run_tests.py
diff --git a/tools/telemetry/telemetry/unittest/run_tests.py b/tools/telemetry/telemetry/unittest/run_tests.py
index ed55b0a1c211ba760be7863ad9109fab71972b27..0a2e3aaedd05c39eac099589b3e3b2d50e57421f 100644
--- a/tools/telemetry/telemetry/unittest/run_tests.py
+++ b/tools/telemetry/telemetry/unittest/run_tests.py
@@ -126,8 +126,8 @@ class RunTestsCommand(command_line.OptparseCommand):
                       dest='run_disabled_tests',
                       action='store_true', default=False,
                       help='Ignore @Disabled and @Enabled restrictions.')
-    parser.add_option('--retry-limit', type='int', default=0,
-                      help='Retry each failure up to N times (default %default)'
+    parser.add_option('--retry-limit', type='int',
+                      help='Retry each failure up to N times'
                            ' to de-flake things.')
     json_results.AddOptions(parser)
 
@@ -136,6 +136,11 @@ class RunTestsCommand(command_line.OptparseCommand):
     if args.verbosity == 0:
       logging.getLogger().setLevel(logging.WARN)
 
+    # We retry failures by default unless we're running a list of tests
+    # explicitly.
+    if args.retry_limit is None and not args.positional_args:
+      args.retry_limit = 3
+
     try:
       possible_browser = browser_finder.FindBrowser(args)
     except browser_finder.BrowserFinderException, ex: