[iOS] Adjust the UserAgent in decidePolicyForNavigationAction

This CL modifies the place where the customUserAgent is updated,
changing it from the request to -decidePolicyForNavigationAction:.
This prevents issues where the page is loaded but not from a request
(for example after a back/forward navigation).

Fixed: 1059235
Change-Id: I83205c80a49e51ebfa194d12bae016bf48b52b4d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2107555
Commit-Queue: Gauthier Ambard <gambard@chromium.org>
Reviewed-by: Ali Juma <ajuma@chromium.org>
Reviewed-by: Eugene But <eugenebut@chromium.org>
Cr-Commit-Position: refs/heads/master@{#754442}

ios/chrome/browser/ui/popup_menu/BUILD.gn

@@ -151,6 +151,7 @@ source_set("eg2_tests") {
   ]
   deps = [
     ":constants",
+    "//base/test:test_support",
     "//components/strings",
     "//ios/chrome/app/strings",
     "//ios/chrome/test/earl_grey:eg_test_support+eg2",
@@ -174,6 +175,7 @@ source_set("eg_tests") {
   ]
   deps = [
     "//base",
+    "//base/test:test_support",
     "//components/strings",
     "//ios/chrome/app/strings",
     "//ios/chrome/browser/ui/popup_menu:constants",

ios/chrome/browser/ui/popup_menu/request_desktop_mobile_site_egtest.mm

@@ -3,6 +3,7 @@
 // found in the LICENSE file.
 
 #include "base/strings/sys_string_conversions.h"
+#import "base/test/ios/wait_util.h"
 #include "components/strings/grit/components_strings.h"
 #import "ios/chrome/browser/ui/popup_menu/popup_menu_constants.h"
 #include "ios/chrome/grit/ios_strings.h"
@@ -31,6 +32,17 @@ const char kMobileSiteLabel[] = "Mobile";
 const char kDesktopSiteLabel[] = "Desktop";
 const char kDesktopPlatformLabel[] = "MacIntel";
 
+// URL to be used when the page needs to be reloaded on back/forward
+// navigations.
+const char kPurgeURL[] = "url-purge.com";
+// JavaScript used to reload the page on back/forward navigations.
+const char kJavaScriptReload[] =
+    "<script>window.onpageshow = function(event) {"
+    "    if (event.persisted) {"
+    "       window.location.href = window.location.href + \"?reloaded\""
+    "    }"
+    "};</script>";
+
 // Custom timeout used when waiting for a web state after requesting desktop
 // or mobile mode.
 const NSTimeInterval kWaitForUserAgentChangeTimeout = 15.0;
@@ -79,15 +91,20 @@ class UserAgentResponseProvider : public web::DataResponseProvider {
       return;
     }
 
+    std::string purge_additions = "";
+    if (request.url.path().find(kPurgeURL) != std::string::npos) {
+      purge_additions = kJavaScriptReload;
+    }
+
     *headers = web::ResponseProvider::GetDefaultResponseHeaders();
     std::string userAgent;
     std::string desktop_user_agent =
         web::BuildUserAgentFromProduct(web::UserAgentType::DESKTOP, "");
     if (request.headers.GetHeader("User-Agent", &userAgent) &&
         userAgent == desktop_user_agent) {
-      response_body->assign("Desktop");
+      response_body->assign(std::string("Desktop\n") + purge_additions);
     } else {
-      response_body->assign("Mobile");
+      response_body->assign(std::string("Mobile\n") + purge_additions);
     }
   }
 };
@@ -168,6 +185,45 @@ class UserAgentResponseProvider : public web::DataResponseProvider {
   [ChromeEarlGrey waitForWebStateContainingText:kMobileSiteLabel];
 }
 
+// Tests that when requesting desktop on another page and coming back to a page
+// that has been purged from memory, we still display the mobile page.
+- (void)testRequestDesktopSiteGoBackToMobilePurged {
+  if (@available(iOS 13, *)) {
+  } else {
+    EARL_GREY_TEST_DISABLED(@"On iOS 12, the User Agent can be wrong when "
+                            @"doing back/forward navigations");
+  }
+
+  std::unique_ptr<web::DataResponseProvider> provider(
+      new UserAgentResponseProvider());
+  web::test::SetUpHttpServer(std::move(provider));
+
+  [ChromeEarlGrey loadURL:web::test::HttpServer::MakeUrl(
+                              "http://" + std::string(kPurgeURL))];
+  // Verify initial reception of the mobile site.
+  [ChromeEarlGrey waitForWebStateContainingText:kMobileSiteLabel];
+
+  [ChromeEarlGrey loadURL:web::test::HttpServer::MakeUrl("http://2.com")];
+
+  // Request and verify reception of the desktop site.
+  [ChromeEarlGreyUI openToolsMenu];
+  [RequestDesktopButton() performAction:grey_tap()];
+  [ChromeEarlGrey waitForWebStateContainingText:kDesktopSiteLabel
+                                        timeout:kWaitForUserAgentChangeTimeout];
+
+  // Verify that going back returns to the mobile site.
+  [[EarlGrey selectElementWithMatcher:chrome_test_util::BackButton()]
+      performAction:grey_tap()];
+  GREYAssert(base::test::ios::WaitUntilConditionOrTimeout(
+                 base::test::ios::kWaitForPageLoadTimeout,
+                 ^bool {
+                   return [ChromeEarlGrey webStateVisibleURL].query() ==
+                          "reloaded";
+                 }),
+             @"Page did not reload");
+  [ChromeEarlGrey waitForWebStateContainingText:kMobileSiteLabel];
+}
+
 // Tests that requesting mobile site of a page works and the user agent
 // propagates to the next navigations in the same tab.
 - (void)testRequestMobileSitePropagatesToNextNavigations {

ios/web/navigation/crw_wk_navigation_handler.mm

@@ -181,6 +181,21 @@ void ReportOutOfSyncURLInDidStartProvisionalNavigation(
     }
   }
 
+  if (item && userAgentType == web::UserAgentType::NONE &&
+      web::GetWebClient()->IsAppSpecificURL(item->GetVirtualURL())) {
+    // In case the URL to be loaded is a WebUI URL and the user agent is nil,
+    // get the mobile user agent.
+    userAgentType = web::UserAgentType::MOBILE;
+  }
+
+  if (userAgentType != web::UserAgentType::NONE) {
+    NSString* userAgentString = base::SysUTF8ToNSString(
+        web::GetWebClient()->GetUserAgent(userAgentType));
+    if (![webView.customUserAgent isEqualToString:userAgentString]) {
+      webView.customUserAgent = userAgentString;
+    }
+  }
+
   WKContentMode contentMode = userAgentType == web::UserAgentType::DESKTOP
                                   ? WKContentModeDesktop
                                   : WKContentModeMobile;

ios/web/web_state/ui/crw_web_request_controller.mm

@@ -573,11 +573,18 @@ enum class BackForwardNavigationType {
     itemUserAgentType = web::UserAgentType::MOBILE;
   }
 
-  if (itemUserAgentType != web::UserAgentType::NONE) {
-    NSString* userAgentString = base::SysUTF8ToNSString(
-        web::GetWebClient()->GetUserAgent(itemUserAgentType));
-    if (![self.webView.customUserAgent isEqualToString:userAgentString]) {
-      self.webView.customUserAgent = userAgentString;
+  if (@available(iOS 13, *)) {
+  } else {
+    // On iOS 13, this is done in
+    // webView:decidePolicyForNavigationAction:preferences:decisionHandler:. As
+    // the method only exists for iOS 13, this check still need to be there for
+    // iOS 12.
+    if (itemUserAgentType != web::UserAgentType::NONE) {
+      NSString* userAgentString = base::SysUTF8ToNSString(
+          web::GetWebClient()->GetUserAgent(itemUserAgentType));
+      if (![self.webView.customUserAgent isEqualToString:userAgentString]) {
+        self.webView.customUserAgent = userAgentString;
+      }
     }
   }