GTTF: add an option to pass test filter using a file

base/test/test_switches.cc

Index: base/test/test_switches.cc
diff --git a/base/test/test_switches.cc b/base/test/test_switches.cc
index f5feaff419bb8243e085708e3433235c5218a29a..d87acaf2308aa6ab5cd8ac0a5c6d1996d8fb8c34 100644
--- a/base/test/test_switches.cc
+++ b/base/test/test_switches.cc
@@ -22,6 +22,9 @@ const char switches::kTestLauncherBotMode[] =
 const char switches::kTestLauncherDebugLauncher[] =
     "test-launcher-debug-launcher";
 
+// Path to file containing test filter (one pattern per line).
+const char switches::kTestLauncherFilterFile[] = "test-launcher-filter-file";
+
 // Number of parallel test launcher jobs.
 const char switches::kTestLauncherJobs[] = "test-launcher-jobs";