WebView: Disable field trial test config

Chrome turns on the studies specified in fieldtrial_testing_config.json
for testing purposes. It doesn't respect the difference between android
and android_webview platforms, so WebView gets all of Android Chrome's
studies enabled, including UseSurfaceLayerForVideo which breaks WebView.
As a workaround, disable the test config.

BUG=853832

Change-Id: Ib8453ac163c7ce71419d25fc5433d3b31b89e894
Reviewed-on: https://chromium-review.googlesource.com/1105608
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Reviewed-by: Bo <boliu@chromium.org>
Commit-Queue: Ilya Sherman <isherman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#568569}

android_webview/browser/aw_field_trial_creator.cc

@@ -28,6 +28,7 @@
 #include "components/variations/seed_response.h"
 #include "components/variations/service/safe_seed_manager.h"
 #include "components/variations/service/variations_service.h"
+#include "components/variations/variations_switches.h"
 
 namespace android_webview {
 namespace {
@@ -63,6 +64,14 @@ AwFieldTrialCreator::AwFieldTrialCreator()
 AwFieldTrialCreator::~AwFieldTrialCreator() {}
 
 void AwFieldTrialCreator::SetUpFieldTrials() {
+  // Workaround for https://crbug.com/853832: In testing, Chrome's experiments
+  // are applied to WebView. Some of these break WebView. So disable the testing
+  // config. TODO(paulmiller): Remove after 853832 is fixed.
+  auto* cmd = base::CommandLine::ForCurrentProcess();
+  if (!cmd->HasSwitch(variations::switches::kDisableFieldTrialTestingConfig)) {
+    cmd->AppendSwitch(variations::switches::kDisableFieldTrialTestingConfig);
+  }
+
   DoSetUpFieldTrials();
 
   // If DoSetUpFieldTrials failed, it might have skipped creating