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

chrome/browser/metrics/metrics_service_uitest.cc

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Tests the MetricsService stat recording to make sure that the numbers are
 // what we expect.
 
 #include <string>
 
 #include "base/file_path.h"
@@ skipping 21 matching lines @@
   MetricsServiceTest() : UITest() {
     // We need to show the window so web content type tabs load.
     show_window_ = true;
   }
 
   // Open a few tabs of random content
   void OpenTabs() {
     scoped_refptr<BrowserProxy> window = automation()->GetBrowserWindow(0);
     ASSERT_TRUE(window.get());
 
-    // The Instant field trial causes a preload of the default search engine,
-    // which messes up the expected page load count. Setting this preference
-    // disables the field trial.
-    ASSERT_TRUE(window->SetBooleanPreference(prefs::kInstantEnabledOnce, true));
-
     FilePath page1_path;
     ASSERT_TRUE(PathService::Get(chrome::DIR_TEST_DATA, &page1_path));
     page1_path = page1_path.AppendASCII("title2.html");
     ASSERT_TRUE(window->AppendTab(net::FilePathToFileURL(page1_path)));
 
     FilePath page2_path;
     ASSERT_TRUE(PathService::Get(chrome::DIR_TEST_DATA, &page2_path));
     page2_path = page2_path.AppendASCII("iframe.html");
     ASSERT_TRUE(window->AppendTab(net::FilePathToFileURL(page2_path)));
   }
@@ skipping 63 matching lines @@
   EXPECT_TRUE(local_state->GetBoolean(prefs::kStabilityExitedCleanly));
   EXPECT_EQ(1, local_state->GetInteger(prefs::kStabilityLaunchCount));
 #if defined(TOUCH_UI)
   // The keyboard page loads for touchui.
   EXPECT_EQ(5, local_state->GetInteger(prefs::kStabilityPageLoadCount));
 #else
   EXPECT_EQ(4, local_state->GetInteger(prefs::kStabilityPageLoadCount));
 #endif
   EXPECT_EQ(1, local_state->GetInteger(prefs::kStabilityRendererCrashCount));
 }