Convert C++ files to Objective-C++ files to remove hack.

In order to remove hack using __OBJC__ to forward-declare an Objective-C
class as a C++ class when the file is included from a C++ file, instead
convert the clients to be Objective-C++ files.

This fixes all clients of
ios/public/provider/chrome/browser/chrome_browser_provider.h.

BUG=298181

Review URL: https://codereview.chromium.org/1706663003

Cr-Commit-Position: refs/heads/master@{#375866}
diff --git a/ios/chrome/browser/BUILD.gn b/ios/chrome/browser/BUILD.gn
index fea7bef1..704811e 100644
--- a/ios/chrome/browser/BUILD.gn
+++ b/ios/chrome/browser/BUILD.gn
@@ -36,8 +36,8 @@
     "autocomplete/autocomplete_scheme_classifier_impl.mm",
     "autocomplete/in_memory_url_index_factory.cc",
     "autocomplete/in_memory_url_index_factory.h",
-    "autocomplete/shortcuts_backend_factory.cc",
     "autocomplete/shortcuts_backend_factory.h",
+    "autocomplete/shortcuts_backend_factory.mm",
     "autofill/form_input_accessory_view.h",
     "autofill/form_input_accessory_view.mm",
     "autofill/form_input_accessory_view_controller.h",
@@ -129,8 +129,8 @@
     "dom_distiller/dom_distiller_service_factory.h",
     "experimental_flags.h",
     "experimental_flags.mm",
-    "favicon/favicon_client_impl.cc",
     "favicon/favicon_client_impl.h",
+    "favicon/favicon_client_impl.mm",
     "favicon/favicon_loader.h",
     "favicon/favicon_loader.mm",
     "favicon/favicon_service_factory.cc",
@@ -228,8 +228,8 @@
     "metrics/ios_chrome_metrics_service_accessor.h",
     "metrics/ios_chrome_metrics_service_client.cc",
     "metrics/ios_chrome_metrics_service_client.h",
-    "metrics/ios_chrome_metrics_services_manager_client.cc",
     "metrics/ios_chrome_metrics_services_manager_client.h",
+    "metrics/ios_chrome_metrics_services_manager_client.mm",
     "metrics/ios_chrome_stability_metrics_provider.cc",
     "metrics/ios_chrome_stability_metrics_provider.h",
     "metrics/mobile_session_shutdown_metrics_provider.h",
@@ -315,8 +315,8 @@
     "services/gcm/ios_chrome_gcm_profile_service_factory.h",
     "sessions/ios_chrome_session_tab_helper.h",
     "sessions/ios_chrome_session_tab_helper.mm",
-    "sessions/ios_chrome_tab_restore_service_client.cc",
     "sessions/ios_chrome_tab_restore_service_client.h",
+    "sessions/ios_chrome_tab_restore_service_client.mm",
     "sessions/ios_chrome_tab_restore_service_factory.cc",
     "sessions/ios_chrome_tab_restore_service_factory.h",
     "signin/about_signin_internals_factory.cc",
@@ -342,12 +342,12 @@
     "signin/gaia_cookie_manager_service_factory.h",
     "signin/ios_chrome_signin_status_metrics_provider_delegate.cc",
     "signin/ios_chrome_signin_status_metrics_provider_delegate.h",
-    "signin/oauth2_token_service_factory.cc",
     "signin/oauth2_token_service_factory.h",
+    "signin/oauth2_token_service_factory.mm",
     "signin/signin_client_factory.cc",
     "signin/signin_client_factory.h",
-    "signin/signin_client_impl.cc",
     "signin/signin_client_impl.h",
+    "signin/signin_client_impl.mm",
     "signin/signin_error_controller_factory.cc",
     "signin/signin_error_controller_factory.h",
     "signin/signin_manager_factory.cc",
@@ -377,8 +377,8 @@
     "sync/glue/sync_start_util.h",
     "sync/ios_chrome_profile_sync_service_factory.cc",
     "sync/ios_chrome_profile_sync_service_factory.h",
-    "sync/ios_chrome_sync_client.cc",
     "sync/ios_chrome_sync_client.h",
+    "sync/ios_chrome_sync_client.mm",
     "sync/ios_chrome_synced_tab_delegate.h",
     "sync/ios_chrome_synced_tab_delegate.mm",
     "sync/sessions/ios_chrome_local_session_event_router.h",
@@ -700,8 +700,8 @@
 source_set("test_support") {
   testonly = true
   sources = [
-    "browser_state/test_chrome_browser_state.cc",
     "browser_state/test_chrome_browser_state.h",
+    "browser_state/test_chrome_browser_state.mm",
     "browser_state/test_chrome_browser_state_isolated_context.h",
     "browser_state/test_chrome_browser_state_isolated_context.mm",
     "browser_state/test_chrome_browser_state_manager.c",
@@ -711,8 +711,8 @@
     "geolocation/test_location_manager.mm",
     "net/mock_image_fetcher.h",
     "net/mock_image_fetcher.mm",
-    "signin/fake_oauth2_token_service_builder.cc",
     "signin/fake_oauth2_token_service_builder.h",
+    "signin/fake_oauth2_token_service_builder.mm",
     "signin/fake_signin_manager_builder.cc",
     "signin/fake_signin_manager_builder.h",
     "sync/fake_sync_service_factory.cc",