Add Accept header to chrome://brave-image loader (#31489)

The PR adds `Accept: <image formats>` to chrome://brave-image requests.
This will allow to use more optimized formats (i.e. WebP) when the backend supports it.

browser/ui/webui/brave_sanitized_image_source.cc

@@ -25,6 +25,7 @@
 #include "net/traffic_annotation/network_traffic_annotation.h"
 #include "services/network/public/cpp/resource_request.h"
 #include "services/network/public/cpp/simple_url_loader.h"
+#include "third_party/blink/public/common/loader/network_utils.h"
 #include "third_party/skia/include/core/SkBitmap.h"
 #include "ui/gfx/codec/png_codec.h"
 #include "ui/gfx/geometry/size.h"
@@ -247,6 +248,8 @@ void BraveSanitizedImageSource::StartImageDownload(
   auto request = std::make_unique<network::ResourceRequest>();
   request->url = request_attributes.image_url;
   request->credentials_mode = network::mojom::CredentialsMode::kOmit;
+  request->headers.SetHeader("Accept",
+                             blink::network_utils::ImageAcceptHeader());
 
   auto loader =
       network::SimpleURLLoader::Create(std::move(request), traffic_annotation);

browser/ui/webui/brave_sanitized_image_source_unittest.cc

@@ -71,7 +71,16 @@ class BraveSanitizedImageSourceTest : public testing::Test {
         "chrome://brave-image/?url=" + EncodeQuery(url.spec()) +
         (target_size.empty() ? ""
                              : "&target_size=" + EncodeQuery(target_size)));
+    base::RepeatingCallback<void(const network::ResourceRequest&)> interceptor =
+        base::BindLambdaForTesting(
+            [&](const network::ResourceRequest& request) {
+              const auto accept_header = request.headers.GetHeader("Accept");
+              ASSERT_TRUE(accept_header.has_value());
+              EXPECT_NE(accept_header->find("image/webp"), std::string::npos);
+            });
+    test_url_loader_factory_.SetInterceptor(std::move(interceptor));
     test_url_loader_factory_.AddResponse(url.spec(), std::move(data));
+
     base::RunLoop run_loop;
     scoped_refptr<base::RefCountedMemory> result;
     source_.StartDataRequest(