Enable only 'downloads' related tests in browser_tests on coverage bot.

tools/code_coverage/coverage_posix.py

Index: tools/code_coverage/coverage_posix.py
===================================================================
--- tools/code_coverage/coverage_posix.py	(revision 169901)
+++ tools/code_coverage/coverage_posix.py	(working copy)
@@ -244,7 +244,27 @@
          'AutomatedUITestBase.DragOut',), },
 }
 
+"""Since random tests are failing/hanging on coverage bot, we are enabling
+   tests feature by feature. crbug.com/159748
+   Below are the downloads related tests enabled.
+   SavePageBrowserTest.*
+   SavePageAsMHTMLBrowserTest.*
+   DownloadQueryTest.*
+   DownloadDangerPromptTest.*
+   DownloadTest.*
+"""
+gTestInclusions = {
+  'linux2': {
+    'browser_tests':
+        ('SavePageBrowserTest.*',
+         'SavePageAsMHTMLBrowserTest.*',
+         'DownloadQueryTest.*',
+         'DownloadDangerPromptTest.*',
+         'DownloadTest.*',),
+  },
+}
 
+
 def TerminateSignalHandler(sig, stack):
   """When killed, try and kill our child processes."""
   signal.signal(sig, signal.SIG_DFL)
@@ -783,6 +803,13 @@
           if test in fulltest:
             negative_gfilter_list += excldict[test]
 
+    inclusions = gTestInclusions
+    include_dict = inclusions.get(sys.platform)
+    if include_dict:
+      for test in include_dict.keys():
+        if test in fulltest:
+          positive_gfilter_list += include_dict[test]
+
     fulltest_basename = os.path.basename(fulltest)
     if fulltest_basename in self.test_filters:
       specific_test_filters = self.test_filters[fulltest_basename].split('-')