Build color_unittests only with flag enabled

Use 'use_color_pipeline' build flag to gate the build and run of
color_unittests.

Since the flag is false by default, remove the unittest from buildbots
for now.

BUG=1003612

Change-Id: Idff6eefb720269e15c60ca69335a5eb0533bd592
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1947225
Reviewed-by: Thomas Lukaszewicz <tluk@chromium.org>
Reviewed-by: Thomas Anderson <thomasanderson@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Wei Li <weili@chromium.org>
Cr-Commit-Position: refs/heads/master@{#721264}

diff --git a/BUILD.gn b/BUILD.gn
index b80b4a5..8c13a45 100644
--- a/BUILD.gn
+++ b/BUILD.gn

@@ -149,7 +149,6 @@
       "//ui/accessibility:accessibility_unittests",
       "//ui/accessibility/extensions:extension_tests",
       "//ui/accessibility/extensions:extensions",
-      "//ui/color:color_unittests",
     ]
   }
 
@@ -812,7 +811,10 @@
   }
 
   if (use_color_pipeline) {
-    deps += [ "//chrome/browser/ui/color:dump_colors" ]
+    deps += [
+      "//chrome/browser/ui/color:dump_colors",
+      "//ui/color:color_unittests",
+    ]
   }
 
   # PFFFT.