PPAPI: Remove threading options; it's always on

build/common.gypi

Index: build/common.gypi
diff --git a/build/common.gypi b/build/common.gypi
index c66369408cc28f598cde5ef6c9b7efe788cbc15f..8e1e40c93241750d31a63318b0f271acc75ec171 100644
--- a/build/common.gypi
+++ b/build/common.gypi
@@ -322,11 +322,6 @@
       # Webrtc compilation is enabled by default. Set to 0 to disable.
       'enable_webrtc%': 1,
 
-      # PPAPI by default does not support plugins making calls off the main
-      # thread. Set to 1 to turn on experimental support for out-of-process
-      # plugins to make call of the main thread.
-      'enable_pepper_threading%': 1,
-
       # Enables use of the session service, which is enabled by default.
       # Support for disabling depends on the platform.
       'enable_session_service%': 1,
@@ -683,7 +678,6 @@
     'use_x11%': '<(use_x11)',
     'use_gnome_keyring%': '<(use_gnome_keyring)',
     'linux_fpic%': '<(linux_fpic)',
-    'enable_pepper_threading%': '<(enable_pepper_threading)',
     'chromeos%': '<(chromeos)',
     'enable_viewport%': '<(enable_viewport)',
     'enable_hidpi%': '<(enable_hidpi)',
@@ -1787,9 +1781,6 @@
       ['proprietary_codecs==1', {
         'defines': ['USE_PROPRIETARY_CODECS'],
       }],
-      ['enable_pepper_threading==1', {
-        'defines': ['ENABLE_PEPPER_THREADING'],
-      }],
       ['enable_viewport==1', {
         'defines': ['ENABLE_VIEWPORT'],
       }],