GTTF: Make it possible to pass sharding settings from command line.

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 18b4881570e671ac6fe7d5223c0e6262022296e1..50b451323946d067089877d423cee9efb8f1ec90 100644
--- a/base/test/test_switches.cc
+++ b/base/test/test_switches.cc
@@ -26,6 +26,15 @@ const char switches::kTestLauncherSummaryOutput[] =
 const char switches::kTestLauncherPrintTestStdio[] =
     "test-launcher-print-test-stdio";
 
+// Index of the test shard to run, starting from 0 (first shard) to total shards
+// minus one (last shard).
+const char switches::kTestLauncherShardIndex[] =
+    "test-launcher-shard-index";
+
+// Total number of shards. Must be the same for all shards.
+const char switches::kTestLauncherTotalShards[] =
+    "test-launcher-total-shards";
+
 // Time (in milliseconds) that the tests should wait before timing out.
 const char switches::kTestLauncherTimeout[] = "test-launcher-timeout";
 // TODO(phajdan.jr): Clean up the switch names.