[test] Fix missing heartbeats in test runner.

TBR=jkummerow@chromium.org

Review URL: https://codereview.chromium.org/1163523008

Cr-Commit-Position: refs/heads/master@{#28808}

tools/testrunner/local/progress.py

@@ -292,6 +292,8 @@ class JUnitTestProgressIndicator(ProgressIndicator):
         test.duration,
         fail_text)
 
+  def Heartbeat(self):
+    self.progress_indicator.Heartbeat()
 
 class JsonTestProgressIndicator(ProgressIndicator):
 
@@ -364,6 +366,9 @@ class JsonTestProgressIndicator(ProgressIndicator):
       "duration": test.duration,
     })
 
+  def Heartbeat(self):
+    self.progress_indicator.Heartbeat()
+
 
 PROGRESS_INDICATORS = {
   'verbose': VerboseProgressIndicator,