Chromecast: enable browser CDMs.

R=lcwu@chromium.org,xhwang@chromium.org
BUG=336640

Review URL: https://codereview.chromium.org/792483002

Cr-Original-Commit-Position: refs/heads/master@{#307541}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: ec45ff1d325cc44fce8c41d59b8235148eb206d5

common.gypi

@@ -1974,7 +1974,7 @@
         'enable_pepper_cdms%': 0,
       }],
 
-      ['OS=="android"', {
+      ['OS=="android" or chromecast==1', {
         'enable_browser_cdms%': 1,
       }, {
         'enable_browser_cdms%': 0,