Image annotation service: added prod server URL.

This change lets Chrome talk to the production image annotation server.

It also includes a bugfix: the experiment feature is changed from
constexpr to const, as suggested here:
https://cs.chromium.org/chromium/src/base/feature_list.h?l=33&rcl=9d2ac606c7193521bef66585a5209fa562d209c4

Bug: 916420
Change-Id: I5fe8f87d4b8b7b8101931476d19e1aecd0d0c8a7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1504655
Commit-Queue: Michael Martis <martis@chromium.org>
Reviewed-by: Jia Meng <jiameng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#637982}

services/image_annotation/image_annotation_service.cc

@@ -12,7 +12,9 @@
 
 namespace image_annotation {
 
-constexpr base::Feature ImageAnnotationService::kExperiment;
+// static
+const base::Feature ImageAnnotationService::kExperiment{
+    "ImageAnnotationServiceExperimental", base::FEATURE_DISABLED_BY_DEFAULT};
 constexpr base::FeatureParam<std::string> ImageAnnotationService::kServerUrl;
 constexpr base::FeatureParam<std::string> ImageAnnotationService::kApiKey;
 constexpr base::FeatureParam<int> ImageAnnotationService::kThrottleMs;

services/image_annotation/image_annotation_service.h

@@ -23,9 +23,8 @@ namespace image_annotation {
 
 class ImageAnnotationService : public service_manager::Service {
  public:
-  // Whether or not to enable service logic for experimentation.
-  static constexpr base::Feature kExperiment{
-      "ImageAnnotationServiceExperimental", base::FEATURE_DISABLED_BY_DEFAULT};
+  // Whether or not to override service parameters for experimentation.
+  static const base::Feature kExperiment;
 
   ImageAnnotationService(
       service_manager::mojom::ServiceRequest request,
@@ -36,10 +35,9 @@ class ImageAnnotationService : public service_manager::Service {
  private:
   // Service params:
 
-  // The service will fail gracefully (i.e. return error codes) when this param
-  // is empty. This ensures graceful behavior when |kExperiment| is disabled.
-  static constexpr base::FeatureParam<std::string> kServerUrl{&kExperiment,
-                                                              "server_url", ""};
+  static constexpr base::FeatureParam<std::string> kServerUrl{
+      &kExperiment, "server_url",
+      "https://ckintersect-pa.googleapis.com/v1/intersect/pixels"};
   // An override Google API key. If empty, the API key with which the browser
   // was built (if any) will be used instead.
   static constexpr base::FeatureParam<std::string> kApiKey{&kExperiment,