Convert //ios/chrome/browser:about_flags to use buildflag_header.

The template buildflag_header allows generating a header file with
defines based on gn variables. This is better than using "defines"
on a target as only the files using the macro will depend on it
instead of all files in the target.

BUG=None

Review-Url: https://codereview.chromium.org/2569663002
Cr-Commit-Position: refs/heads/master@{#437858}

ios/chrome/browser/BUILD.gn

@@ -2,6 +2,7 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+import("//build/buildflag_header.gni")
 import("//build/config/features.gni")
 import("//build/config/ios/rules.gni")
 import("//third_party/protobuf/proto_library.gni")
@@ -21,6 +22,8 @@ declare_args() {
 
 source_set("browser") {
   sources = [
+    "about_flags.h",
+    "about_flags.mm",
     "app_startup_parameters.h",
     "app_startup_parameters.mm",
     "application_context.cc",
@@ -74,10 +77,14 @@ source_set("browser") {
     "xcallback_parameters.mm",
   ]
   deps = [
+    ":google_api_keys_header",
     ":settings_resources",
     "//base",
     "//components/autofill/core/browser",
     "//components/autofill/core/common",
+    "//components/dom_distiller/core",
+    "//components/flags_ui",
+    "//components/flags_ui:switches",
     "//components/gcm_driver",
     "//components/handoff",
     "//components/keyed_service/core",
@@ -95,12 +102,16 @@ source_set("browser") {
     "//components/search_engines",
     "//components/signin/core/browser",
     "//components/ssl_config",
+    "//components/strings",
+    "//components/sync",
     "//components/translate/core/browser",
     "//components/url_formatter",
     "//components/variations",
     "//components/variations/service",
     "//components/version_info",
     "//components/webdata_services",
+    "//google_apis",
+    "//ios/chrome/app/strings",
     "//ios/chrome/browser/browser_state",
     "//ios/chrome/browser/sync/glue",
     "//ios/chrome/common",
@@ -128,7 +139,6 @@ source_set("browser_impl") {
     "ios_chrome_main_parts.mm",
   ]
   deps = [
-    ":about_flags",
     ":browser",
     "//base",
     "//components/component_updater",
@@ -180,35 +190,9 @@ source_set("browser_impl") {
   }
 }
 
-# This is a separate target so that the 'defines' does not leak to the
-# other files (which would increase the compilation time when changing
-# the value).
-source_set("about_flags") {
-  configs += [ "//build/config/compiler:enable_arc" ]
-  sources = [
-    "about_flags.h",
-    "about_flags.mm",
-  ]
-
-  deps = [
-    ":browser",
-    "//base",
-    "//components/autofill/core/common",
-    "//components/dom_distiller/core",
-    "//components/flags_ui",
-    "//components/flags_ui:switches",
-    "//components/ntp_tiles",
-    "//components/reading_list/core",
-    "//components/strings",
-    "//components/sync",
-    "//components/variations",
-    "//google_apis",
-    "//ios/chrome/app/strings",
-    "//ios/web",
-    "//ios/web:user_agent",
-  ]
-
-  defines = [
+buildflag_header("google_api_keys_header") {
+  header = "google_api_keys.h"
+  flags = [
     "GOOGLE_STAGING_API_URL=\"$google_staging_api_url\"",
     "GOOGLE_STAGING_LSO_URL=\"$google_staging_lso_url\"",
     "GOOGLE_TEST_API_URL=\"$google_test_api_url\"",

ios/chrome/browser/about_flags.mm

@@ -31,6 +31,7 @@
 #include "components/sync/driver/sync_driver_switches.h"
 #include "google_apis/gaia/gaia_switches.h"
 #include "ios/chrome/browser/chrome_switches.h"
+#include "ios/chrome/browser/google_api_keys.h"
 #include "ios/chrome/grit/ios_strings.h"
 #include "ios/web/public/user_agent.h"
 #include "ios/web/public/web_view_creation_util.h"
@@ -39,10 +40,6 @@
 #include "components/variations/variations_switches.h"
 #endif
 
-#if !defined(__has_feature) || !__has_feature(objc_arc)
-#error "This file requires ARC support."
-#endif
-
 namespace {
 // To add a new entry, add to the end of kFeatureEntries. There are two
 // distinct types of entries:
@@ -79,19 +76,22 @@ void AppendSwitchesFromExperimentalSettings(base::CommandLine* command_line) {
   NSString* gaia_environment = [defaults stringForKey:kGAIAEnvironment];
   if ([gaia_environment isEqualToString:@"Staging"]) {
     command_line->AppendSwitchASCII(switches::kGoogleApisUrl,
-                                    GOOGLE_STAGING_API_URL);
-    command_line->AppendSwitchASCII(switches::kLsoUrl, GOOGLE_STAGING_LSO_URL);
+                                    BUILDFLAG(GOOGLE_STAGING_API_URL));
+    command_line->AppendSwitchASCII(switches::kLsoUrl,
+                                    BUILDFLAG(GOOGLE_STAGING_LSO_URL));
   } else if ([gaia_environment isEqualToString:@"Test"]) {
-    command_line->AppendSwitchASCII(switches::kGaiaUrl, GOOGLE_TEST_OAUTH_URL);
+    command_line->AppendSwitchASCII(switches::kGaiaUrl,
+                                    BUILDFLAG(GOOGLE_TEST_OAUTH_URL));
     command_line->AppendSwitchASCII(switches::kGoogleApisUrl,
-                                    GOOGLE_TEST_API_URL);
-    command_line->AppendSwitchASCII(switches::kLsoUrl, GOOGLE_TEST_LSO_URL);
+                                    BUILDFLAG(GOOGLE_TEST_API_URL));
+    command_line->AppendSwitchASCII(switches::kLsoUrl,
+                                    BUILDFLAG(GOOGLE_TEST_LSO_URL));
     command_line->AppendSwitchASCII(switches::kSyncServiceURL,
-                                    GOOGLE_TEST_SYNC_URL);
+                                    BUILDFLAG(GOOGLE_TEST_SYNC_URL));
     command_line->AppendSwitchASCII(switches::kOAuth2ClientID,
-                                    GOOGLE_TEST_OAUTH_CLIENT_ID);
+                                    BUILDFLAG(GOOGLE_TEST_OAUTH_CLIENT_ID));
     command_line->AppendSwitchASCII(switches::kOAuth2ClientSecret,
-                                    GOOGLE_TEST_OAUTH_CLIENT_SECRET);
+                                    BUILDFLAG(GOOGLE_TEST_OAUTH_CLIENT_SECRET));
   }
 
   // Populate command line flag for the Tab Switcher experiment from the

ios/chrome/browser/ui/webui/BUILD.gn

@@ -38,7 +38,6 @@ source_set("webui") {
     "//google_apis",
     "//ios/chrome/app/strings",
     "//ios/chrome/browser",
-    "//ios/chrome/browser:about_flags",
     "//ios/chrome/browser/browser_state",
     "//ios/chrome/browser/crash_report",
     "//ios/chrome/browser/metrics",