Switch from build-time to run-time flags for Project Spitzer.

media/media_variables.gypi

Index: media/media_variables.gypi
diff --git a/media/media_variables.gypi b/media/media_variables.gypi
index b203ca09d67e6f2f2d403919a5f1a2d94364b699..8b47003554ef1f6764b84f9691f6e1e1f07f2684 100644
--- a/media/media_variables.gypi
+++ b/media/media_variables.gypi
@@ -7,16 +7,18 @@
   'variables': {
     'conditions': [
       ['OS == "android" or OS == "ios"', {
-        # Android and iOS don't use FFmpeg, libvpx nor libwebm by default.
-        # Set media_use_ffmpeg=1 for Android builds to compile experimental
-        # support for FFmpeg and the desktop media pipeline.
+        # Android and iOS don't use libwebm by default.
+        'media_use_libwebm%': 0,
+      }, {
+        'media_use_libwebm%': 1,
+      }],
+      ['OS == "ios"', {
+        # iOS doesn't use FFmpeg or libvpx by default.
         'media_use_ffmpeg%': 0,
         'media_use_libvpx%': 0,
-        'media_use_libwebm%': 0,
       }, {
         'media_use_ffmpeg%': 1,
         'media_use_libvpx%': 1,
-        'media_use_libwebm%': 1,
       }],
     ],
   },