Do not instantiate base::FieldTrialList explicitly in tests

The test suite already instantiates a FieldTrialList as per
https://chromium-review.googlesource.com/c/chromium/src/+/1883567 so
it's no longer necessary to do so explicitly in tests.

This patch addresses unit tests under:
/chrome/browser/password_manager

This CL was uploaded by git cl split.

R=dvadym@chromium.org

Bug: 1018667
Change-Id: I977fb12a0fb0fedb897a804d306fc1b755ff6653
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1917524
Auto-Submit: Mikel Astiz <mastiz@chromium.org>
Reviewed-by: Vadym Doroshenko <dvadym@chromium.org>
Commit-Queue: Vadym Doroshenko <dvadym@chromium.org>
Cr-Commit-Position: refs/heads/master@{#715639}

chrome/browser/password_manager/chrome_password_manager_client_unittest.cc

@@ -12,7 +12,6 @@
 #include "base/bind.h"
 #include "base/command_line.h"
 #include "base/macros.h"
-#include "base/metrics/field_trial.h"
 #include "base/run_loop.h"
 #include "base/strings/string16.h"
 #include "base/strings/stringprintf.h"
@@ -200,8 +199,7 @@ std::unique_ptr<KeyedService> CreateTestSyncService(
 
 class ChromePasswordManagerClientTest : public ChromeRenderViewHostTestHarness {
  public:
-  ChromePasswordManagerClientTest()
-      : field_trial_list_(nullptr), metrics_enabled_(false) {}
+  ChromePasswordManagerClientTest() : metrics_enabled_(false) {}
   void SetUp() override;
   void TearDown() override;
 
@@ -237,7 +235,6 @@ class ChromePasswordManagerClientTest : public ChromeRenderViewHostTestHarness {
   FakePasswordAutofillAgent fake_agent_;
 
   TestingPrefServiceSimple prefs_;
-  base::FieldTrialList field_trial_list_;
   bool metrics_enabled_;
 };