AshColorProvider: update kButtonLabel/IconColorPrimary.

The spec was wrong before. Now update the two colors according to the
corrected spec.

Bug: 972162
Change-Id: I898c33b186af5d8543c2516eb44db85c504aae48
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2354726Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Xiaoqian Dai <xdai@chromium.org>
Cr-Commit-Position: refs/heads/master@{#798682}

ash/style/ash_color_provider.cc

@@ -359,8 +359,8 @@ SkColor AshColorProvider::GetContentLayerColorImpl(
       break;
     case ContentLayerType::kButtonLabelColorPrimary:
     case ContentLayerType::kButtonIconColorPrimary:
-      light_color = gfx::kGoogleRed900;
-      dark_color = gfx::kGoogleRed200;
+      light_color = gfx::kGoogleGrey900;
+      dark_color = gfx::kGoogleGrey200;
       break;
     case ContentLayerType::kSliderThumbColorDisabled:
       light_color = gfx::kGoogleGrey600;