[iOS] Upstream switches and flags controlling which WebView is used

ios/chrome/browser/experimental_flags.mm

 // Copyright 2015 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.
 
 // This file can be empty. Its purpose is to contain the relatively short lived
 // definitions required for experimental flags.
 
 #include "ios/chrome/browser/experimental_flags.h"
 
 #include <string>
 
 #include "base/command_line.h"
 #include "base/metrics/field_trial.h"
 #include "base/strings/string_number_conversions.h"
+#include "base/strings/string_util.h"
 #include "components/variations/variations_associated_data.h"
 #include "ios/chrome/browser/chrome_switches.h"
+#include "ios/web/public/web_view_util.h"
 
 namespace {
 NSString* const kEnableAlertOnBackgroundUpload =
     @"EnableAlertsOnBackgroundUpload";
 }  // namespace
 
 namespace experimental_flags {
 
 bool IsAlertOnBackgroundUploadEnabled() {
   return [[NSUserDefaults standardUserDefaults]
       boolForKey:kEnableAlertOnBackgroundUpload];
 }
 
 bool IsOpenFromClipboardEnabled() {
   base::CommandLine* command_line = base::CommandLine::ForCurrentProcess();
   return command_line->HasSwitch(switches::kEnableIOSOpenFromClipboard);
 }
 
+bool IsWKWebViewEnabled() {
+  // If WKWebView isn't supported, don't activate the experiment at all. This
+  // avoids someone being slotted into the WKWebView bucket (and thus reporting
+  // as WKWebView), but actually running UIWebView.
+  if (!web::IsWKWebViewSupported())
+    return false;
+
+  std::string group_name =
+      base::FieldTrialList::FindFullName("IOSUseWKWebView");
+
+  // First check if the experimental flag is turned on.
+  base::CommandLine* command_line = base::CommandLine::ForCurrentProcess();
+  if (command_line->HasSwitch(switches::kEnableIOSWKWebView)) {
+    return true;
+  } else if (command_line->HasSwitch(switches::kDisableIOSWKWebView)) {
+    return false;
+  }
+
+  // Check if the finch experiment is turned on.
+  return StartsWithASCII(group_name, "Enabled", false);
+}
+
 size_t MemoryWedgeSizeInMB() {
   std::string wedge_size_string;
 
   // Get the size from the Experimental setting.
   base::CommandLine* command_line = base::CommandLine::ForCurrentProcess();
   wedge_size_string =
       command_line->GetSwitchValueASCII(switches::kIOSMemoryWedgeSize);
 
   // Otherwise, get from a variation param.
   if (wedge_size_string.empty()) {
     wedge_size_string =
         variations::GetVariationParamValue("MemoryWedge", "wedge_size");
   }
 
   // Parse the value.
   size_t wedge_size_in_mb = 0;
   if (base::StringToSizeT(wedge_size_string, &wedge_size_in_mb))
     return wedge_size_in_mb;
   return 0;
 }
 
 }  // namespace experimental_flags