[NTP] Adds service integration to request photos.

Adds a service request and callback to get Google Photos from an album.
An access token for the signed-in user with requisite scope is
obtained and used in the request.

Bug: 839152
Change-Id: I3b012b8cdba247d94052c774dd0b1ae1be070d14
Reviewed-on: https://chromium-review.googlesource.com/1114231Reviewed-by: Christian Dullweber <dullweber@chromium.org>
Reviewed-by: Alexei Svitkine <asvitkine@chromium.org>
Reviewed-by: Marc Treib <treib@chromium.org>
Commit-Queue: Ramya Nagarajan <ramyan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#574442}

chrome/browser/search/background/ntp_background.proto

@@ -110,3 +110,30 @@ message PersonalAlbumsResponse {
   // Set to true if there was an error on the server.
   optional bool error_on_server = 5;
 }
+
+// The Photos API returns metadata about photos within an album as a
+// SettingPreviewResponse. See NtpBackgroundService::FetchAlbumPhotos for the
+// API's usage. This is a server-defined message.
+message SettingPreviewResponse {
+  // Deprecated or unused tag numbers
+  reserved 1;
+
+  // A preview image for each photo.
+  message Preview { optional string preview_url = 1; }
+  repeated Preview preview = 2;
+
+  // A resume token can be used to get the next page of results.
+  optional string resume_token = 3;
+
+  // An error_msg is set when the status is not 'SUCCESS'.
+  optional ErrorCode status = 4 [default = SUCCESS];
+  optional string error_msg = 5;
+}
+
+// Server-defined ErrorCodes for the Photos API.
+enum ErrorCode {
+  UNKNOWN = 0;
+  SUCCESS = 1;
+  BAD_REQUEST = 2;
+  SERVER_ERROR = 3;
+}

chrome/browser/search/background/ntp_background_data.cc

@@ -106,3 +106,27 @@ AlbumInfo AlbumInfo::CreateFromProto(
 
   return album_info;
 }
+
+AlbumPhoto::AlbumPhoto() = default;
+// TODO(crbug.com/851990) Handle urls with existing image options.
+AlbumPhoto::AlbumPhoto(const std::string& photo_url,
+                       const std::string& default_image_options)
+    : thumbnail_photo_url(GURL(photo_url)),
+      photo_url(GURL(photo_url + ((photo_url.find('=') == std::string::npos)
+                                      ? default_image_options
+                                      : std::string()))) {}
+AlbumPhoto::AlbumPhoto(const AlbumPhoto&) = default;
+AlbumPhoto::AlbumPhoto(AlbumPhoto&&) = default;
+AlbumPhoto::~AlbumPhoto() = default;
+
+AlbumPhoto& AlbumPhoto::operator=(const AlbumPhoto&) = default;
+AlbumPhoto& AlbumPhoto::operator=(AlbumPhoto&&) = default;
+
+bool operator==(const AlbumPhoto& lhs, const AlbumPhoto& rhs) {
+  return lhs.thumbnail_photo_url == rhs.thumbnail_photo_url &&
+         lhs.photo_url == rhs.photo_url;
+}
+
+bool operator!=(const AlbumPhoto& lhs, const AlbumPhoto& rhs) {
+  return !(lhs == rhs);
+}

chrome/browser/search/background/ntp_background_data.h

@@ -87,9 +87,12 @@ struct AlbumInfo {
 
   static AlbumInfo CreateFromProto(const ntp::background::AlbumMetaData& album);
 
-  // A unique identifier for the album.
+  // A unique identifier for the album. This is required when requesting the
+  // album.
   int64_t album_id;
-  // A generic photo container ID based on the photo provider.
+  // A generic photo container ID based on the photo provider. For Google
+  // Photos, this corresponds to media keys for the collection. It is also
+  // required when requesting the album.
   std::string photo_container_id;
   // A human-readable name for the album.
   std::string album_name;
@@ -100,4 +103,27 @@ struct AlbumInfo {
 bool operator==(const AlbumInfo& lhs, const AlbumInfo& rhs);
 bool operator!=(const AlbumInfo& lhs, const AlbumInfo& rhs);
 
+// Represents a photo within an album.
+struct AlbumPhoto {
+  AlbumPhoto();
+  // default_image_options are applied to the image.image_url() if options
+  // (specifying resolution, cropping, etc) are not already present.
+  AlbumPhoto(const std::string& photo_url,
+             const std::string& default_image_options);
+  AlbumPhoto(const AlbumPhoto&);
+  AlbumPhoto(AlbumPhoto&&);
+  ~AlbumPhoto();
+
+  AlbumPhoto& operator=(const AlbumPhoto&);
+  AlbumPhoto& operator=(AlbumPhoto&&);
+
+  // The thumbnail image URL, typically lower resolution than the photo_url.
+  GURL thumbnail_photo_url;
+  // The image URL.
+  GURL photo_url;
+};
+
+bool operator==(const AlbumPhoto& lhs, const AlbumPhoto& rhs);
+bool operator!=(const AlbumPhoto& lhs, const AlbumPhoto& rhs);
+
 #endif  // CHROME_BROWSER_SEARCH_BACKGROUND_NTP_BACKGROUND_DATA_H_

chrome/browser/search/background/ntp_background_service.h

@@ -15,6 +15,7 @@
 #include "chrome/browser/search/background/ntp_background_data.h"
 #include "chrome/browser/search/background/ntp_background_service_observer.h"
 #include "components/keyed_service/core/keyed_service.h"
+#include "net/base/url_util.h"
 #include "url/gurl.h"
 
 class GoogleServiceAuthError;
@@ -39,6 +40,7 @@ class NtpBackgroundService : public KeyedService {
       const base::Optional<GURL>& collections_api_url_override,
       const base::Optional<GURL>& collection_images_api_url_override,
       const base::Optional<GURL>& albums_api_url_override,
+      const base::Optional<GURL>& photos_api_base_url_override,
       const base::Optional<std::string>& image_options_override);
   ~NtpBackgroundService() override;
 
@@ -61,6 +63,13 @@ class NtpBackgroundService : public KeyedService {
   // called on the observers.
   void FetchAlbumInfo();
 
+  // Initially requests an access token for the signed-in user, and then
+  // requests an asynchronous fetch of photos using the access token, if it is
+  // available. After the fetch completes, OnAlbumPhotosAvailable will be called
+  // on the observers.
+  void FetchAlbumPhotos(const std::string& album_id,
+                        const std::string& photo_container_id);
+
   // Add/remove observers. All observers must unregister themselves before the
   // NtpBackgroundService is destroyed.
   void AddObserver(NtpBackgroundServiceObserver* observer);
@@ -79,21 +88,29 @@ class NtpBackgroundService : public KeyedService {
   // Returns the currently cached AlbumInfo, if any.
   const std::vector<AlbumInfo>& album_info() const { return album_info_; }
 
+  // Returns the currently cached AlbumPhotos, if any.
+  const std::vector<AlbumPhoto>& album_photos() const { return album_photos_; }
+
   GURL GetCollectionsLoadURLForTesting() const;
   GURL GetImagesURLForTesting() const;
   GURL GetAlbumsURLForTesting() const;
+  GURL GetAlbumPhotosApiUrlForTesting(
+      const std::string& album_id,
+      const std::string& photo_container_id) const;
 
  private:
   GURL collections_api_url_;
   GURL collection_images_api_url_;
   GURL albums_api_url_;
+  GURL photos_api_base_url_;
   std::string image_options_;
 
   // Used to download the proto from the Backdrop service.
   scoped_refptr<network::SharedURLLoaderFactory> url_loader_factory_;
   std::unique_ptr<network::SimpleURLLoader> collections_loader_;
-  std::unique_ptr<network::SimpleURLLoader> image_info_loader_;
+  std::unique_ptr<network::SimpleURLLoader> collections_image_info_loader_;
   std::unique_ptr<network::SimpleURLLoader> albums_loader_;
+  std::unique_ptr<network::SimpleURLLoader> albums_photo_info_loader_;
 
   identity::IdentityManager* const identity_manager_;
   // The current OAuth2 token fetcher.
@@ -112,22 +129,36 @@ class NtpBackgroundService : public KeyedService {
   void OnCollectionImageInfoFetchComplete(
       const std::unique_ptr<std::string> response_body);
 
-  void GetAccessTokenCallback(GoogleServiceAuthError error, std::string token);
+  void GetAccessTokenForAlbumCallback(GoogleServiceAuthError error,
+                                      std::string token);
 
   // Callback that processes the response from the FetchAlbumInfo request,
   // refreshing the contents of album_info_ with server-provided data.
   void OnAlbumInfoFetchComplete(
       const std::unique_ptr<std::string> response_body);
 
+  void GetAccessTokenForPhotosCallback(GoogleServiceAuthError error,
+                                       std::string token);
+
+  // Callback that processes the response from SettingPreviewRequest, refreshing
+  // the contents of album_photos_ with server-provided data.
+  void OnAlbumPhotosFetchComplete(
+      const std::unique_ptr<std::string> response_body);
+
   enum class FetchComplete {
     // Indicates that asynchronous fetch of CollectionInfo has completed.
     COLLECTION_INFO,
     // Indicates that asynchronous fetch of CollectionImages has completed.
     COLLECTION_IMAGE_INFO,
     // Indicates that asynchronous fetch of AlbumInfo has completed.
-    ALBUM_INFO
+    ALBUM_INFO,
+    // Indicates that asynchronous fetch of AlbumPhotos has completed.
+    ALBUM_PHOTOS
   };
   void NotifyObservers(FetchComplete fetch_complete);
+  GURL GetAlbumPhotosApiUrl() const;
+  GURL FormatAlbumPhotosBaseApiUrl(const std::string& album_id,
+                                   const std::string& photo_container_id) const;
 
   std::vector<CollectionInfo> collection_info_;
 
@@ -136,6 +167,10 @@ class NtpBackgroundService : public KeyedService {
 
   std::vector<AlbumInfo> album_info_;
 
+  std::vector<AlbumPhoto> album_photos_;
+  std::string requested_album_id_;
+  std::string requested_photo_container_id_;
+
   DISALLOW_COPY_AND_ASSIGN(NtpBackgroundService);
 };
 

chrome/browser/search/background/ntp_background_service_factory.cc

@@ -51,11 +51,14 @@ KeyedService* NtpBackgroundServiceFactory::BuildServiceInstanceFor(
           features::kNtpBackgrounds, "background-collection-images-api-url");
   std::string albums_api_url = base::GetFieldTrialParamValueByFeature(
       features::kNtpBackgrounds, "background-albums-api-url");
+  std::string photos_api_base_url = base::GetFieldTrialParamValueByFeature(
+      features::kNtpBackgrounds, "background-photos-api-url");
   std::string image_options = base::GetFieldTrialParamValueByFeature(
       features::kNtpBackgrounds, "background-collections-image-options");
   base::Optional<GURL> collection_api_url_override;
   base::Optional<GURL> collection_images_api_url_override;
   base::Optional<GURL> albums_api_url_override;
+  base::Optional<GURL> photos_api_base_url_override;
   base::Optional<std::string> image_options_override;
   if (!collections_api_url.empty()) {
     collection_api_url_override = GURL(collections_api_url);
@@ -66,6 +69,9 @@ KeyedService* NtpBackgroundServiceFactory::BuildServiceInstanceFor(
   if (!albums_api_url.empty()) {
     albums_api_url_override = GURL(albums_api_url);
   }
+  if (!photos_api_base_url.empty()) {
+    photos_api_base_url_override = GURL(photos_api_base_url);
+  }
   if (!image_options.empty()) {
     image_options_override = image_options;
   }
@@ -80,5 +86,5 @@ KeyedService* NtpBackgroundServiceFactory::BuildServiceInstanceFor(
   return new NtpBackgroundService(
       identity_manager, url_loader_factory, collection_api_url_override,
       collection_images_api_url_override, albums_api_url_override,
-      image_options_override);
+      photos_api_base_url_override, image_options_override);
 }

chrome/browser/search/background/ntp_background_service_observer.h

@@ -9,26 +9,25 @@
 class NtpBackgroundServiceObserver {
  public:
   // Called when the CollectionInfo is updated, usually as the result of a
-  // FetchCollectionInfo() call on the service. Note that this is called after
-  // each FetchCollectionInfo(), even if the network request failed, or if it
-  // didn't result in an actual change to the cached data. You can get the new
-  // data via NtpBackgroundService::collection_info().
+  // FetchCollectionInfo() call on the service. You can get the new data via
+  // NtpBackgroundService::collection_info().
   virtual void OnCollectionInfoAvailable() = 0;
 
   // Called when the CollectionImages are updated, usually as the result of a
-  // FetchCollectionImageInfo() call on the service. Note that this is called
-  // after each FetchCollectionImage(), even if the network request failed, or
-  // if it didn't result in an actual change to the cached data. You can get the
-  // new data via NtpBackgroundService::collection_images().
+  // FetchCollectionImageInfo() call on the service. You can get the new data
+  // via NtpBackgroundService::collection_images().
   virtual void OnCollectionImagesAvailable() = 0;
 
   // Called when the AlbumInfo is updated, usually as the result of a
-  // PersonalAlbumsRequestOption() call on the service. Note that this is called
-  // after each FetchAlbumInfo(), even if the network request failed, or if it
-  // didn't result in an actual change to the cached data. You can get the new
+  // PersonalAlbumsRequestOption() call on the service. You can get the new
   // data via NtpBackgroundService::album_info().
   virtual void OnAlbumInfoAvailable() = 0;
 
+  // Called when the AlbumPhotos are updated, usually as the result of a
+  // SettingPreviewRequest() call on the service. You can get the new data via
+  // NtpBackgroundService::album_photos().
+  virtual void OnAlbumPhotosAvailable() = 0;
+
   // Called when the OnNtpBackgroundService is shutting down. Observers that
   // might outlive the service should use this to unregister themselves, and
   // clear out any pointers to the service they might hold.

chrome/browser/search/background/ntp_background_service_unittest.cc

@@ -20,6 +20,7 @@
 #include "url/gurl.h"
 
 using testing::Eq;
+using testing::StartsWith;
 
 namespace {
 
@@ -46,7 +47,8 @@ class NtpBackgroundServiceTest : public testing::Test {
 
     service_ = std::make_unique<NtpBackgroundService>(
         identity_env_.identity_manager(), test_shared_loader_factory_,
-        base::nullopt, base::nullopt, base::nullopt, kImageOptions);
+        base::nullopt, base::nullopt, base::nullopt, base::nullopt,
+        kImageOptions);
   }
 
   void SetUpResponseWithData(const GURL& load_url,
@@ -80,11 +82,10 @@ TEST_F(NtpBackgroundServiceTest, CollectionInfoNetworkError) {
 
   ASSERT_TRUE(service()->collection_info().empty());
 
-  base::RunLoop loop;
   service()->FetchCollectionInfo();
-  loop.RunUntilIdle();
+  base::RunLoop().RunUntilIdle();
 
-  ASSERT_TRUE(service()->collection_info().empty());
+  EXPECT_TRUE(service()->collection_info().empty());
 }
 
 TEST_F(NtpBackgroundServiceTest, BadCollectionsResponse) {
@@ -93,9 +94,8 @@ TEST_F(NtpBackgroundServiceTest, BadCollectionsResponse) {
 
   ASSERT_TRUE(service()->collection_info().empty());
 
-  base::RunLoop loop;
   service()->FetchCollectionInfo();
-  loop.RunUntilIdle();
+  base::RunLoop().RunUntilIdle();
 
   EXPECT_TRUE(service()->collection_info().empty());
 }
@@ -115,9 +115,8 @@ TEST_F(NtpBackgroundServiceTest, GoodCollectionsResponse) {
 
   ASSERT_TRUE(service()->collection_info().empty());
 
-  base::RunLoop loop;
   service()->FetchCollectionInfo();
-  loop.RunUntilIdle();
+  base::RunLoop().RunUntilIdle();
 
   CollectionInfo collection_info;
   collection_info.collection_id = collection.collection_id();
@@ -133,11 +132,10 @@ TEST_F(NtpBackgroundServiceTest, CollectionImagesNetworkError) {
 
   ASSERT_TRUE(service()->collection_images().empty());
 
-  base::RunLoop loop;
   service()->FetchCollectionImageInfo("shapes");
-  loop.RunUntilIdle();
+  base::RunLoop().RunUntilIdle();
 
-  ASSERT_TRUE(service()->collection_images().empty());
+  EXPECT_TRUE(service()->collection_images().empty());
 }
 
 TEST_F(NtpBackgroundServiceTest, BadCollectionImagesResponse) {
@@ -146,9 +144,8 @@ TEST_F(NtpBackgroundServiceTest, BadCollectionImagesResponse) {
 
   ASSERT_TRUE(service()->collection_images().empty());
 
-  base::RunLoop loop;
   service()->FetchCollectionImageInfo("shapes");
-  loop.RunUntilIdle();
+  base::RunLoop().RunUntilIdle();
 
   EXPECT_TRUE(service()->collection_images().empty());
 }
@@ -168,9 +165,8 @@ TEST_F(NtpBackgroundServiceTest, GoodCollectionImagesResponse) {
 
   ASSERT_TRUE(service()->collection_images().empty());
 
-  base::RunLoop loop;
   service()->FetchCollectionImageInfo("shapes");
-  loop.RunUntilIdle();
+  base::RunLoop().RunUntilIdle();
 
   CollectionImage collection_image;
   collection_image.collection_id = "shapes";
@@ -211,12 +207,11 @@ TEST_F(NtpBackgroundServiceTest, MultipleRequests) {
   ASSERT_TRUE(service()->collection_info().empty());
   ASSERT_TRUE(service()->collection_images().empty());
 
-  base::RunLoop loop;
   service()->FetchCollectionInfo();
   service()->FetchCollectionImageInfo("shapes");
   // Subsequent requests are ignored while the loader is in use.
   service()->FetchCollectionImageInfo("colors");
-  loop.RunUntilIdle();
+  base::RunLoop().RunUntilIdle();
 
   CollectionInfo collection_info;
   collection_info.collection_id = collection.collection_id();
@@ -241,11 +236,10 @@ TEST_F(NtpBackgroundServiceTest, AlbumInfoNetworkError) {
 
   ASSERT_TRUE(service()->album_info().empty());
 
-  base::RunLoop loop;
   service()->FetchAlbumInfo();
-  loop.RunUntilIdle();
+  base::RunLoop().RunUntilIdle();
 
-  ASSERT_TRUE(service()->album_info().empty());
+  EXPECT_TRUE(service()->album_info().empty());
 }
 
 TEST_F(NtpBackgroundServiceTest, BadAlbumsResponse) {
@@ -254,9 +248,8 @@ TEST_F(NtpBackgroundServiceTest, BadAlbumsResponse) {
 
   ASSERT_TRUE(service()->album_info().empty());
 
-  base::RunLoop loop;
   service()->FetchAlbumInfo();
-  loop.RunUntilIdle();
+  base::RunLoop().RunUntilIdle();
 
   EXPECT_TRUE(service()->album_info().empty());
 }
@@ -276,9 +269,8 @@ TEST_F(NtpBackgroundServiceTest, GoodAlbumsResponse) {
 
   ASSERT_TRUE(service()->album_info().empty());
 
-  base::RunLoop loop;
   service()->FetchAlbumInfo();
-  loop.RunUntilIdle();
+  base::RunLoop().RunUntilIdle();
 
   AlbumInfo album_info;
   album_info.album_id = album.album_id();
@@ -289,3 +281,71 @@ TEST_F(NtpBackgroundServiceTest, GoodAlbumsResponse) {
   EXPECT_FALSE(service()->album_info().empty());
   EXPECT_THAT(service()->album_info().at(0), Eq(album_info));
 }
+
+TEST_F(NtpBackgroundServiceTest, AlbumPhotosNetworkError) {
+  SetUpResponseWithNetworkError(service()->GetAlbumPhotosApiUrlForTesting(
+      "album_id", "photo_container_id"));
+
+  ASSERT_TRUE(service()->album_photos().empty());
+
+  service()->FetchAlbumPhotos("album_id", "photo_container_id");
+  base::RunLoop().RunUntilIdle();
+
+  EXPECT_TRUE(service()->album_photos().empty());
+}
+
+TEST_F(NtpBackgroundServiceTest, BadAlbumPhotosResponse) {
+  SetUpResponseWithData(service()->GetAlbumPhotosApiUrlForTesting(
+                            "album_id", "photo_container_id"),
+                        "bad serialized SettingPreviewResponse");
+
+  ASSERT_TRUE(service()->album_photos().empty());
+
+  service()->FetchAlbumPhotos("album_id", "photo_container_id");
+  base::RunLoop().RunUntilIdle();
+
+  EXPECT_TRUE(service()->album_photos().empty());
+}
+
+TEST_F(NtpBackgroundServiceTest, AlbumPhotoErrorResponse) {
+  ntp::background::SettingPreviewResponse response;
+  response.set_status(ntp::background::ErrorCode::SERVER_ERROR);
+  response.set_error_msg("server error");
+  std::string response_string;
+  response.SerializeToString(&response_string);
+
+  SetUpResponseWithData(service()->GetAlbumPhotosApiUrlForTesting(
+                            "album_id", "photo_container_id"),
+                        response_string);
+
+  ASSERT_TRUE(service()->album_photos().empty());
+
+  service()->FetchAlbumPhotos("album_id", "photo_container_id");
+  base::RunLoop().RunUntilIdle();
+
+  EXPECT_TRUE(service()->album_photos().empty());
+}
+
+TEST_F(NtpBackgroundServiceTest, GoodAlbumPhotosResponse) {
+  ntp::background::SettingPreviewResponse::Preview preview;
+  preview.set_preview_url("https://wallpapers.co/some_image");
+  ntp::background::SettingPreviewResponse response;
+  *response.add_preview() = preview;
+  std::string response_string;
+  response.SerializeToString(&response_string);
+
+  SetUpResponseWithData(service()->GetAlbumPhotosApiUrlForTesting(
+                            "album_id", "photo_container_id"),
+                        response_string);
+
+  ASSERT_TRUE(service()->album_photos().empty());
+
+  service()->FetchAlbumPhotos("album_id", "photo_container_id");
+  base::RunLoop().RunUntilIdle();
+
+  EXPECT_FALSE(service()->album_photos().empty());
+  EXPECT_THAT(service()->album_photos().at(0).thumbnail_photo_url.spec(),
+              StartsWith(preview.preview_url()));
+  EXPECT_THAT(service()->album_photos().at(0).photo_url.spec(),
+              StartsWith(preview.preview_url()));
+}

chrome/browser/search/local_ntp_source.cc

@@ -321,6 +321,20 @@ base::Value ConvertAlbumInfoToDict(const std::vector<AlbumInfo>& album_info) {
   return albums;
 }
 
+base::Value ConvertAlbumPhotosToDict(
+    const std::vector<AlbumPhoto>& album_photos) {
+  base::Value photos(base::Value::Type::LIST);
+  photos.GetList().reserve(album_photos.size());
+  for (const AlbumPhoto& photo : album_photos) {
+    base::Value dict(base::Value::Type::DICTIONARY);
+    dict.SetKey("thumbnail_photo_url",
+                base::Value(photo.thumbnail_photo_url.spec()));
+    dict.SetKey("photo_url", base::Value(photo.photo_url.spec()));
+    photos.GetList().push_back(std::move(dict));
+  }
+  return photos;
+}
+
 std::unique_ptr<base::DictionaryValue> ConvertOGBDataToDict(
     const OneGoogleBarData& og) {
   auto result = std::make_unique<base::DictionaryValue>();
@@ -673,7 +687,7 @@ void LocalNtpSource::StartDataRequest(
                                                    callback);
       ntp_background_service_->FetchAlbumInfo();
     } else {
-      // If there's no "collection_type" param, default to getting collections.
+      // If collection_type is not "album", default to getting collections.
       // TODO(ramyan): Explicitly require a collection_type when frontend
       //  supports it.
       ntp_background_collections_requests_.emplace_back(base::TimeTicks::Now(),
@@ -688,6 +702,28 @@ void LocalNtpSource::StartDataRequest(
       callback.Run(nullptr);
       return;
     }
+    std::string collection_type_param;
+    GURL path_url = GURL(chrome::kChromeSearchLocalNtpUrl).Resolve(path);
+    if (net::GetValueForKeyInQuery(path_url, "collection_type",
+                                   &collection_type_param) &&
+        (collection_type_param == "album")) {
+      std::string album_id_param;
+      std::string photo_container_id_param;
+      if (!net::GetValueForKeyInQuery(path_url, "album_id", &album_id_param) ||
+          !net::GetValueForKeyInQuery(path_url, "photo_container_id",
+                                      &photo_container_id_param)) {
+        callback.Run(nullptr);
+        return;
+      }
+      ntp_background_photos_requests_.emplace_back(base::TimeTicks::Now(),
+                                                   callback);
+      ntp_background_service_->FetchAlbumPhotos(album_id_param,
+                                                photo_container_id_param);
+    } else {
+      // If collection_type is not "album", default to getting images for a
+      // collection.
+      // TODO(ramyan): Explicitly require a collection_type when frontend
+      // supports it.
       std::string collection_id_param;
       GURL path_url = GURL(chrome::kChromeSearchLocalNtpUrl).Resolve(path);
       if (net::GetValueForKeyInQuery(path_url, "collection_id",
@@ -698,6 +734,7 @@ void LocalNtpSource::StartDataRequest(
       } else {
         callback.Run(nullptr);
       }
+    }
     return;
   }
 
@@ -916,6 +953,30 @@ void LocalNtpSource::OnAlbumInfoAvailable() {
   ntp_background_albums_requests_.clear();
 }
 
+void LocalNtpSource::OnAlbumPhotosAvailable() {
+  DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
+
+  if (ntp_background_photos_requests_.empty())
+    return;
+
+  scoped_refptr<base::RefCountedString> result;
+  std::string js;
+  base::JSONWriter::Write(
+      ConvertAlbumPhotosToDict(ntp_background_service_->album_photos()), &js);
+  js = "var photos = " + js + ";";
+  result = base::RefCountedString::TakeString(&js);
+
+  base::TimeTicks now = base::TimeTicks::Now();
+  for (const auto& request : ntp_background_photos_requests_) {
+    request.callback.Run(result);
+    base::TimeDelta delta = now - request.start_time;
+    UMA_HISTOGRAM_MEDIUM_TIMES(
+        "NewTabPage.BackgroundService.Photos.RequestLatency", delta);
+    // TODO(ramyan): Define and capture latency for failed requests.
+  }
+  ntp_background_photos_requests_.clear();
+}
+
 void LocalNtpSource::OnNtpBackgroundServiceShuttingDown() {
   DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
 

chrome/browser/search/local_ntp_source.h

@@ -92,6 +92,7 @@ class LocalNtpSource : public content::URLDataSource,
   void OnCollectionInfoAvailable() override;
   void OnCollectionImagesAvailable() override;
   void OnAlbumInfoAvailable() override;
+  void OnAlbumPhotosAvailable() override;
   void OnNtpBackgroundServiceShuttingDown() override;
 
   // Overridden from OneGoogleBarServiceObserver:
@@ -105,6 +106,7 @@ class LocalNtpSource : public content::URLDataSource,
   std::vector<NtpBackgroundRequest> ntp_background_collections_requests_;
   std::vector<NtpBackgroundRequest> ntp_background_image_info_requests_;
   std::vector<NtpBackgroundRequest> ntp_background_albums_requests_;
+  std::vector<NtpBackgroundRequest> ntp_background_photos_requests_;
 
   NtpBackgroundService* ntp_background_service_;
 

tools/metrics/histograms/histograms.xml

@@ -59101,6 +59101,16 @@ uploading your change for review.
   </summary>
 </histogram>
 
+<histogram name="NewTabPage.BackgroundService.Photos.RequestLatency" units="ms"
+    expires_after="M74">
+  <owner>ramyan@chromium.org</owner>
+  <owner>yyushkina@chromium.org</owner>
+  <summary>
+    The time it took until a request from the New Tab Page for Google Photos (in
+    a specific album) was served.
+  </summary>
+</histogram>
+
 <histogram name="NewTabPage.BookmarkActionAndroid"
     enum="NewTabPageBookmarkActionAndroid">
   <obsolete>

tools/traffic_annotation/summary/annotations.xml

@@ -123,6 +123,7 @@ Refer to README.md for content description and update process.
  <item id="gcm_unregistration" hash_code="119542033" type="0" content_hash_code="30144127" os_list="linux,windows" file_path="google_apis/gcm/engine/unregistration_request.cc"/>
  <item id="geo_language_provider" hash_code="52821843" type="1" second_id="96590038" content_hash_code="104675663" os_list="linux,windows" semantics_fields="1" policy_fields="3,4" file_path="components/language/content/browser/geo_language_provider.cc"/>
  <item id="google_photos_album_names_download" hash_code="65075134" type="0" content_hash_code="124531309" os_list="linux,windows" file_path="chrome/browser/search/background/ntp_background_service.cc"/>
+ <item id="google_photos_metadata_download" hash_code="93441068" type="0" content_hash_code="48786223" os_list="linux,windows" file_path="chrome/browser/search/background/ntp_background_service.cc"/>
  <item id="google_url_tracker" hash_code="5492492" type="0" content_hash_code="54474899" os_list="linux,windows" file_path="components/google/core/browser/google_url_tracker.cc"/>
  <item id="headless_url_request" hash_code="29865866" type="0" deprecated="2018-07-10" content_hash_code="76700151" file_path=""/>
  <item id="history_notice_utils_notice" hash_code="102595701" type="1" second_id="110307337" content_hash_code="130829410" os_list="linux,windows" semantics_fields="2,3,4" policy_fields="4" file_path="components/browsing_data/core/history_notice_utils.cc"/>