Fixes gn-check errors with enable_plugins=false.

chrome/common/BUILD.gn

Index: chrome/common/BUILD.gn
diff --git a/chrome/common/BUILD.gn b/chrome/common/BUILD.gn
index b49e24c84988adc71a8e448baaae5cb49d764b43..acc2361cbaae3ebca7ec52bee2e4efda0ac842d7 100644
--- a/chrome/common/BUILD.gn
+++ b/chrome/common/BUILD.gn
@@ -150,8 +150,6 @@ static_library("common") {
     "url_constants.h",
     "web_application_info.cc",
     "web_application_info.h",
-    "widevine_cdm_constants.cc",
-    "widevine_cdm_constants.h",
   ]
   defines = []
 
@@ -479,6 +477,12 @@ static_library("common") {
       "pepper_permission_util.h",
     ]
   }
+  if (enable_pepper_cdms) {
+    sources += [
+      "widevine_cdm_constants.cc",
+      "widevine_cdm_constants.h",
+    ]
+  }
   if (!enable_webrtc) {
     sources -= [ "media/webrtc_logging_messages.h" ]
   }