Fix duplication of UkmSamplingRate feature instance

This patch fixes the crash on debugging build when visiting chrome://ukm
due to CheckFeatureIdentity(UkmSamplingRate) failure.
COMPONENT_EXPORT makes the definition of the base::Feature
UkmSamplingRate from ukm_recorder_impl.cc exported and shared by the
libraries that reference it, ensuring there's only one copy of the
base::Feature in memory.

Bug-id: b/160004246
Change-Id: Icda0e0a403538a263f8132afc19dd0cb455395db
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2274240
Commit-Queue: Yue Ru Sun <yrsun@chromium.org>
Reviewed-by: Steven Holte <holte@chromium.org>
Cr-Commit-Position: refs/heads/master@{#784145}

chrome/browser/metrics/ukm_browsertest.cc

@@ -49,6 +49,7 @@
 #include "components/version_info/version_info.h"
 #include "content/public/browser/browsing_data_remover.h"
 #include "content/public/common/content_switches.h"
+#include "content/public/common/url_constants.h"
 #include "content/public/test/browser_test.h"
 #include "content/public/test/browser_test_utils.h"
 #include "content/public/test/browsing_data_remover_test_util.h"
@@ -1441,4 +1442,26 @@ IN_PROC_BROWSER_TEST_F(UkmBrowserTest, NotMarkSourcesIfNavigationNotCommitted) {
 }
 #endif  // !defined(OS_ANDROID)
 
+#if !defined(OS_ANDROID)
+IN_PROC_BROWSER_TEST_F(UkmBrowserTest, DebugUiRenders) {
+  MetricsConsentOverride metrics_consent(true);
+
+  Profile* profile = ProfileManager::GetActiveUserProfile();
+  std::unique_ptr<ProfileSyncServiceHarness> harness =
+      EnableSyncForProfile(profile);
+  PlatformBrowser browser = CreatePlatformBrowser(profile);
+
+  ukm::UkmService* ukm_service(GetUkmService());
+  EXPECT_TRUE(ukm_service->IsSamplingEnabled());
+
+  // chrome://ukm
+  const GURL debug_url(content::GetWebUIURLString(content::kChromeUIUkmHost));
+
+  content::TestNavigationObserver waiter(debug_url);
+  waiter.WatchExistingWebContents();
+  EXPECT_TRUE(ui_test_utils::NavigateToURL(browser, debug_url));
+  waiter.WaitForNavigationFinished();
+}
+#endif  // !defined(OS_ANDROID)
+
 }  // namespace metrics

components/ukm/BUILD.gn

@@ -4,6 +4,35 @@
 
 import("//testing/test.gni")
 
+component("ukm_recorder") {
+  output_name = "ukm_recorder"
+
+  defines = [ "IS_UKM_RECORDER_IMPL" ]
+
+  friend = [
+    ":test_support",
+    ":unit_tests",
+  ]
+
+  sources = [
+    "scheme_constants.cc",
+    "scheme_constants.h",
+    "ukm_entry_filter.h",
+    "ukm_recorder_impl.cc",
+    "ukm_recorder_impl.h",
+  ]
+
+  deps = [
+    "//base",
+    "//components/variations",
+    "//services/metrics/public/cpp:metrics_cpp",
+    "//services/metrics/public/cpp:ukm_builders",
+    "//services/metrics/public/mojom",
+    "//third_party/metrics_proto",
+    "//url",
+  ]
+}
+
 # The Url-Keyed Metrics (UKM) service is responsible for gathering and
 # uploading reports that contain fine grained performance metrics including
 # URLs for top-level navigations.
@@ -13,13 +42,8 @@ static_library("ukm") {
     "app_source_url_recorder.h",
     "field_trials_provider_helper.cc",
     "field_trials_provider_helper.h",
-    "scheme_constants.cc",
-    "scheme_constants.h",
-    "ukm_entry_filter.h",
     "ukm_pref_names.cc",
     "ukm_pref_names.h",
-    "ukm_recorder_impl.cc",
-    "ukm_recorder_impl.h",
     "ukm_reporting_service.cc",
     "ukm_reporting_service.h",
     "ukm_rotation_scheduler.cc",
@@ -31,6 +55,7 @@ static_library("ukm") {
   ]
 
   public_deps = [
+    ":ukm_recorder",
     "//services/metrics/public/cpp:metrics_cpp",
     "//services/metrics/public/cpp:ukm_builders",
     "//services/metrics/public/mojom",

components/ukm/scheme_constants.h

@@ -5,15 +5,20 @@
 #ifndef COMPONENTS_UKM_SCHEME_CONSTANTS_H_
 #define COMPONENTS_UKM_SCHEME_CONSTANTS_H_
 
+#include "base/component_export.h"
+
 namespace ukm {
 
 // Defines several URL scheme constants to avoid dependencies.
 // kAppScheme will be defined in code that isn't available here.
+COMPONENT_EXPORT(UKM_RECORDER)
 extern const char kAppScheme[];
 // kChromeUIScheme is defined in content, which this code can't depend on
 // since it's used by iOS too.
+COMPONENT_EXPORT(UKM_RECORDER)
 extern const char kChromeUIScheme[];
 // kExtensionScheme is defined in extensions which also isn't available here.
+COMPONENT_EXPORT(UKM_RECORDER)
 extern const char kExtensionScheme[];
 
 }  // namespace ukm

components/ukm/ukm_recorder_impl.cc

@@ -9,6 +9,7 @@
 #include <unordered_map>
 #include <utility>
 
+#include "base/component_export.h"
 #include "base/feature_list.h"
 #include "base/metrics/crc32.h"
 #include "base/metrics/field_trial.h"
@@ -33,11 +34,12 @@
 
 namespace ukm {
 
-namespace {
-
+COMPONENT_EXPORT(UKM_RECORDER)
 const base::Feature kUkmSamplingRateFeature{"UkmSamplingRate",
                                             base::FEATURE_DISABLED_BY_DEFAULT};
 
+namespace {
+
 // Gets the list of whitelisted Entries as string. Format is a comma separated
 // list of Entry names (as strings).
 std::string GetWhitelistEntries() {

components/ukm/ukm_recorder_impl.h

@@ -14,6 +14,7 @@
 #include <vector>
 
 #include "base/callback_forward.h"
+#include "base/component_export.h"
 #include "base/containers/flat_map.h"
 #include "base/containers/flat_set.h"
 #include "base/sequence_checker.h"
@@ -39,7 +40,7 @@ namespace debug {
 class UkmDebugDataExtractor;
 }
 
-class UkmRecorderImpl : public UkmRecorder {
+class COMPONENT_EXPORT(UKM_RECORDER) UkmRecorderImpl : public UkmRecorder {
   using IsWebstoreExtensionCallback =
       base::RepeatingCallback<bool(base::StringPiece id)>;
 

components/ukm/ukm_service.cc

@@ -24,6 +24,7 @@
 #include "components/prefs/pref_service.h"
 #include "components/ukm/scheme_constants.h"
 #include "components/ukm/ukm_pref_names.h"
+#include "components/ukm/ukm_recorder_impl.h"
 #include "components/ukm/ukm_rotation_scheduler.h"
 #include "services/metrics/public/cpp/delegating_ukm_recorder.h"
 #include "third_party/metrics_proto/ukm/report.pb.h"