lacros: Add user-agent override hack for netflix.com.

This CL adds a hack to blink that causes Lacros to user the Linux user
agent for netflix.com instead of the ChromeOS user agent. This allows
Lacros users to watch Netflix. A proper solution is blocked on the CDM
team, ETA Q2 2021.

Bug: 1114866
Change-Id: I8b510a9c0886d7f472d932416d60ad404093384c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2521140
Commit-Queue: Erik Chen <erikchen@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#825088}

content/renderer/BUILD.gn

@@ -269,6 +269,7 @@ target(link_target_type, "renderer") {
     "//base",
     "//base:i18n",
     "//build:chromecast_buildflags",
+    "//build:chromeos_buildflags",
     "//cc",
     "//cc/animation",
     "//cc/mojo_embedder",

content/renderer/render_frame_impl.cc

@@ -48,6 +48,7 @@
 #include "base/time/time.h"
 #include "base/trace_event/trace_event.h"
 #include "build/build_config.h"
+#include "build/chromeos_buildflags.h"
 #include "cc/base/switches.h"
 #include "content/common/associated_interfaces.mojom.h"
 #include "content/common/content_constants_internal.h"
@@ -4850,6 +4851,21 @@ blink::WebString RenderFrameImpl::UserAgentOverride() {
     return WebString::FromUTF8(render_view_->GetRendererPreferences()
                                    .user_agent_override.ua_string_override);
   }
+
+#if BUILDFLAG(IS_LACROS)
+  // TODO(https://crbug.com/1114866): Implement proper L3 CDM support for
+  // Lacros. This is scheduled for Q2 2021. After that we can remove this hack.
+  WebSecurityOrigin frame_origin = frame_->GetDocument().GetSecurityOrigin();
+  if (frame_origin.Host().Utf8() == "www.netflix.com") {
+    WebString user_agent = RenderThreadImpl::current()->GetUserAgent();
+    std::string user_agent_utf8 =
+        user_agent.Utf8(WebString::UTF8ConversionMode::kStrict);
+    base::ReplaceSubstringsAfterOffset(&user_agent_utf8, /*start_offset=*/0,
+                                       " CrOS ", " Linux ");
+    return WebString::FromUTF8(user_agent_utf8);
+  }
+#endif
+
   return blink::WebString();
 }