[iOS] Freeze Safari version in Mobile UserAgent

This CL freezes the Safari version in the Mobile User Agent, aligning with
https://blog.chromium.org/2019/05/improving-privacy-and-security-on-web.html.

It will also increase compatibility with WebKit, as it is frozen in
WebKit mobile User Agent.

The iOS 12 version was introduced in http://crrev.com/c/1102485.
This CL was made during the beta version of iOS 12, my guess is that the
version was frozen in WebKit before the Stable version was released, so we
released a wrong version by mistake.

Bug: 1026615
Change-Id: I7641bc54327f3d135501dc47c365c4458ca8dace
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1926488
Commit-Queue: Gauthier Ambard <gambard@chromium.org>
Reviewed-by: Aaron Tagliaboschi <aarontag@chromium.org>
Reviewed-by: Peter Lee <pkl@chromium.org>
Reviewed-by: Eugene But <eugenebut@chromium.org>
Cr-Commit-Position: refs/heads/master@{#720198}

ios/web/common/user_agent.mm

@@ -95,20 +95,12 @@ std::string BuildUserAgentFromProduct(UserAgentType type,
   if (type == web::UserAgentType::DESKTOP)
     return kDesktopUserAgent;
 
-  std::string safari_version;
-  if (@available(iOS 13, *)) {
-    safari_version = "604.1";
-  } else {
-    safari_version = "605.1";
-  }
-
   DCHECK_EQ(web::UserAgentType::MOBILE, type);
   std::string user_agent;
   base::StringAppendF(&user_agent,
                       "Mozilla/5.0 (%s) AppleWebKit/605.1.15"
-                      " (KHTML, like Gecko) %s Mobile/15E148 Safari/%s",
-                      BuildOSCpuInfo(type).c_str(), product.c_str(),
-                      safari_version.c_str());
+                      " (KHTML, like Gecko) %s Mobile/15E148 Safari/604.1",
+                      BuildOSCpuInfo(type).c_str(), product.c_str());
 
   return user_agent;
 }

ios/web/common/user_agent_unittest.mm

@@ -70,20 +70,12 @@ TEST_F(UserAgentTest, MobileUserAgentForProduct) {
       &os_major_version, &os_minor_version, &os_bugfix_version);
   base::StringAppendF(&os_version, "%d_%d", os_major_version, os_minor_version);
 
-  std::string safari_version;
-  if (@available(iOS 13, *)) {
-    safari_version = "604.1";
-  } else {
-    safari_version = "605.1";
-  }
-
   std::string expected_user_agent;
   base::StringAppendF(
       &expected_user_agent,
       "Mozilla/5.0 (%s; CPU %s %s like Mac OS X) AppleWebKit/605.1.15 (KHTML, "
-      "like Gecko) %s Mobile/15E148 Safari/%s",
-      platform.c_str(), cpu.c_str(), os_version.c_str(), product.c_str(),
-      safari_version.c_str());
+      "like Gecko) %s Mobile/15E148 Safari/604.1",
+      platform.c_str(), cpu.c_str(), os_version.c_str(), product.c_str());
 
   std::string result =
       BuildUserAgentFromProduct(web::UserAgentType::MOBILE, product);