Update EnterpriseStartupDialog text color

Using ChromeTypographyProvider to set the color instead of hard coding.
Normal mode keeps using kGoogleGrey700. Dark mode use kGoogleGrey500.

Before: https://drive.google.com/open?id=1qGdPgomtoXVPkAZ4XZr5gzd5ckBcfLzz
After: https://drive.google.com/open?id=1MZ4wt7LW68CK-KqzLKgLKuZNNUBcrS59

Bug: 990406
Change-Id: I4f088d4d49e4b0df0b467b1f195dcd16f08aa84d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1732480Reviewed-by: Peter Boström <pbos@chromium.org>
Commit-Queue: Owen Min <zmin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#684072}

chrome/browser/ui/views/policy/enterprise_startup_dialog_view.cc

@@ -56,7 +56,9 @@ std::unique_ptr<views::Label> CreateText(const base::string16& message) {
   auto text = std::make_unique<views::Label>(message);
   text->SetFontList(gfx::FontList().Derive(kFontSizeDelta, gfx::Font::NORMAL,
                                            gfx::Font::Weight::MEDIUM));
-  text->SetEnabledColor(gfx::kGoogleGrey700);
+  text->SetEnabledColor(
+      views::style::GetColor(*text, views::style::CONTEXT_MESSAGE_BOX_BODY_TEXT,
+                             views::style::STYLE_PRIMARY));
   text->SetLineHeight(kLineHeight);
   return text;
 }