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}

BUILD.gn

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

testing/buildbot/chrome.json

@@ -1187,23 +1187,6 @@
         },
         "test": "chromeos_unittests"
       },
-      {
-        "merge": {
-          "args": [],
-          "script": "//testing/merge_scripts/standard_gtest_merge.py"
-        },
-        "swarming": {
-          "can_use_on_swarming_builders": true,
-          "dimension_sets": [
-            {
-              "os": "Ubuntu-16.04",
-              "pool": "chrome.tests",
-              "ssd": "0"
-            }
-          ]
-        },
-        "test": "color_unittests"
-      },
       {
         "merge": {
           "args": [],

testing/buildbot/chromium.chromiumos.json

@@ -1123,21 +1123,6 @@
         },
         "test": "chromeos_unittests"
       },
-      {
-        "merge": {
-          "args": [],
-          "script": "//testing/merge_scripts/standard_gtest_merge.py"
-        },
-        "swarming": {
-          "can_use_on_swarming_builders": true,
-          "dimension_sets": [
-            {
-              "os": "Ubuntu-16.04"
-            }
-          ]
-        },
-        "test": "color_unittests"
-      },
       {
         "merge": {
           "args": [],
@@ -2592,22 +2577,6 @@
         },
         "test": "chromeos_unittests"
       },
-      {
-        "isolate_coverage_data": true,
-        "merge": {
-          "args": [],
-          "script": "//testing/merge_scripts/standard_gtest_merge.py"
-        },
-        "swarming": {
-          "can_use_on_swarming_builders": true,
-          "dimension_sets": [
-            {
-              "os": "Ubuntu-16.04"
-            }
-          ]
-        },
-        "test": "color_unittests"
-      },
       {
         "isolate_coverage_data": true,
         "merge": {