Extract constant files target from infobars_ui target

Extract constant files to a separate target from infobars_ui target. So
that EG2 tests can include only the constants target to access the
constants, without pulling app related targets.

Bug: 917114, 987646

Change-Id: Ic79579d955e84f8c6ae0b6c524280f0b6893bd01
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1842613Reviewed-by: Sergio Collazos <sczs@chromium.org>
Reviewed-by: Rohit Rao <rohitrao@chromium.org>
Commit-Queue: Zhaoyang Li <zhaoyangli@chromium.org>
Cr-Commit-Position: refs/heads/master@{#703428}

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

@@ -37,6 +37,14 @@ source_set("public") {
   ]
 }
 
+source_set("constants") {
+  configs += [ "//build/config/compiler:enable_arc" ]
+  sources = [
+    "infobar_constants.h",
+    "infobar_constants.mm",
+  ]
+}
+
 source_set("feature_flags") {
   configs += [ "//build/config/compiler:enable_arc" ]
   sources = [
@@ -54,8 +62,6 @@ source_set("infobars_ui") {
     "confirm_infobar_view.h",
     "confirm_infobar_view.mm",
     "infobar_badge_ui_delegate.h",
-    "infobar_constants.h",
-    "infobar_constants.mm",
     "infobar_container_consumer.h",
     "infobar_ui_delegate.h",
     "legacy_infobar_container_view_controller.h",
@@ -89,6 +95,9 @@ source_set("infobars_ui") {
     "//ui/gfx",
     "//url",
   ]
+  public_deps = [
+    ":constants",
+  ]
   libs = [
     "CoreGraphics.framework",
     "QuartzCore.framework",