Allow controlling the Instant field trial through a command line flag.

chrome/test/base/test_launcher_utils.cc

Index: chrome/test/base/test_launcher_utils.cc
diff --git a/chrome/test/base/test_launcher_utils.cc b/chrome/test/base/test_launcher_utils.cc
index 4dfe1f74ac176b69811eaba6cf0d59ac4c607a5c..d8239eb00f5921620c69a762efc65fa53325dfbd 100644
--- a/chrome/test/base/test_launcher_utils.cc
+++ b/chrome/test/base/test_launcher_utils.cc
@@ -53,6 +53,9 @@ void PrepareBrowserCommandLineForTests(CommandLine* command_line) {
   // See crbug.com/89808.
   // command_line->AppendSwitch(switches::kUseMockKeychain);
 #endif
+
+  // Disable the Instant field trial, which may cause unexpected page loads.
+  command_line->AppendSwitchASCII(switches::kInstantFieldTrial, "disabled");
 }
 
 bool OverrideUserDataDir(const FilePath& user_data_dir) {