Move ENABLE_PEPPER_CDMS to a buildflag header.

chrome/test/BUILD.gn

Index: chrome/test/BUILD.gn
diff --git a/chrome/test/BUILD.gn b/chrome/test/BUILD.gn
index 0bbc1e9d61867585402bf7d9936b9fc5428745d2..63d6c2539699d2063ff9b6f3befb4fff4b50ee76 100644
--- a/chrome/test/BUILD.gn
+++ b/chrome/test/BUILD.gn
@@ -13,6 +13,7 @@ import("//chrome/test/base/js2gtest.gni")
 import("//components/os_crypt/features.gni")
 import("//services/shell/public/service_manifest.gni")
 import("//testing/test.gni")
+import("//third_party/widevine/cdm/widevine.gni")
 import("//v8/gni/v8.gni")
 
 if (is_android) {
@@ -2891,6 +2892,7 @@ if (!is_android) {
       "//base/test:test_support_perf",
       "//testing/gtest",
       "//testing/perf",
+      "//third_party/widevine/cdm:cdm_features",
       "//third_party/widevine/cdm:version_h",
     ]
 
@@ -3424,6 +3426,7 @@ test("unit_tests") {
     "//third_party/cacheinvalidation",
     "//third_party/icu",
     "//third_party/libxml",
+    "//third_party/widevine/cdm:cdm_features",
     "//ui/base:test_support",
     "//ui/display:test_support",
     "//ui/gfx:test_support",