Tell grit 2x scale is supported when enable_hidpi is set.

To avoid decreasing the supported platforms from today, this expands
enable_hidpi from Linux (incl. CrOS)/Mac/Win to also include iOS.

Bug: 564112
Change-Id: I246ea0dd25d93a174195489c2e388e3c7a890e8c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1670357
Commit-Queue: Peter Kasting <pkasting@chromium.org>
Reviewed-by: Rohit Rao <rohitrao@chromium.org>
Reviewed-by: Robert Flack <flackr@chromium.org>
Reviewed-by: Sadrul Chowdhury <sadrul@chromium.org>
Cr-Commit-Position: refs/heads/master@{#672639}

tools/grit/grit_rule.gni

@@ -98,6 +98,7 @@ import("//build/config/features.gni")
 import("//build/config/ui.gni")
 import("//build/toolchain/gcc_toolchain.gni")  # For enable_resource_whitelist_generation
 import("//third_party/closure_compiler/closure_args.gni")
+import("//ui/base/ui_features.gni")
 if (enable_resource_whitelist_generation) {
   assert(target_os == "android" || target_os == "win",
          "unsupported platform for resource whitelist generation")
@@ -108,6 +109,13 @@ if (enable_resource_whitelist_generation) {
 
 grit_defines = []
 
+if (enable_hidpi) {
+  grit_defines += [
+    "-D",
+    "scale_factors=2x",
+  ]
+}
+
 # Mac and iOS want Title Case strings.
 use_titlecase_in_grd_files = is_mac || is_ios
 if (use_titlecase_in_grd_files) {
@@ -137,8 +145,6 @@ if (is_chromeos) {
   grit_defines += [
     "-D",
     "chromeos",
-    "-D",
-    "scale_factors=2x",
   ]
 }
 
@@ -184,13 +190,6 @@ if (is_android) {
   ]
 }
 
-if (is_mac || is_ios) {
-  grit_defines += [
-    "-D",
-    "scale_factors=2x",
-  ]
-}
-
 # When cross-compiling, explicitly pass the target system to grit.
 if (current_toolchain != host_toolchain) {
   if (is_android) {

ui/base/ui_features.gni

@@ -12,7 +12,7 @@ declare_args() {
   has_native_accessibility = use_atk || is_win || is_mac
 
   # Whether the message center should be included for displaying notifications.
-  enable_message_center = is_win || is_mac || is_linux || is_chromeos
+  enable_message_center = is_win || is_mac || is_linux
 }
 
-enable_hidpi = is_mac || is_win || is_linux
+enable_hidpi = is_mac || is_win || is_linux || is_ios