Tell grit 2x scale is supported on the same platforms as enable_hidpi.

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

This is a reland of
https://chromium-review.googlesource.com/c/chromium/src/+/1670357 , which was
reverted since a direct dependency on ui_features.gni breaks external projects.

Bug: 564112
Change-Id: I2426ccae4eaf300a1fe8df77bccb3ec2e932ee01
TBR: rohitrao, sadrul
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1681302
Auto-Submit: Peter Kasting <pkasting@chromium.org>
Reviewed-by: Rohit Rao <rohitrao@chromium.org>
Reviewed-by: Robert Flack <flackr@chromium.org>
Commit-Queue: Robert Flack <flackr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#673348}

tools/grit/grit_rule.gni

@@ -108,6 +108,13 @@ if (enable_resource_whitelist_generation) {
 
 grit_defines = []
 
+if (is_mac || is_win || is_linux || is_ios) {
+  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 +144,6 @@ if (is_chromeos) {
   grit_defines += [
     "-D",
     "chromeos",
-    "-D",
-    "scale_factors=2x",
   ]
 }
 
@@ -184,13 +189,6 @@ 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