Move ENABLE_PEPPER_CDMS to a buildflag header.

third_party/widevine/cdm/widevine.gni

Index: third_party/widevine/cdm/widevine.gni
diff --git a/third_party/widevine/cdm/widevine.gni b/third_party/widevine/cdm/widevine.gni
index b10a92b47494fe4954df89e40b9e4e80a12fb653..1f93ac0a0b34c0a5692552a86e1c68a2027a574f 100644
--- a/third_party/widevine/cdm/widevine.gni
+++ b/third_party/widevine/cdm/widevine.gni
@@ -2,7 +2,16 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+import("//build/config/features.gni")
+
 declare_args() {
   # Allow widevinecdmadapter to be built in Chromium.
   enable_widevine = false
 }
+
+# Enables the use of CDMs in pepper plugins.
+#
+# This is available as a buildflag for C++ preprocessor, see
+# //third_party/widevine/cdm:cdm_features.
+enable_pepper_cdms =
+    enable_plugins && (is_linux || is_mac || is_win) && !is_chromecast

[jrummell, 2016/10/10 22:45:57]

Why did you put the flag in third_party/widevine/cdm? For testing we also build
ExternalClearKey (see media/cdm/ppapi/BUILD.gn). I think media/cdm/ppapi/ is a
better place to put the flag, since that is where all the Chromium code to
handle pepper plugins is located. (Plus when we complete the switch to mojo,
widevine will remain but the code in media/cdm/ppapi/ should disappear).

[brettw, 2016/10/10 23:43:42]

Good idea, done.