Skia: Add Command Buffer support to Linux/Mac

Code added to load libcommand_buffer_gles2.so on linux or
mac.

Review URL: https://codereview.chromium.org/1346423002
diff --git a/gyp/common_variables.gypi b/gyp/common_variables.gypi
index e8a8355..57fad1d 100644
--- a/gyp/common_variables.gypi
+++ b/gyp/common_variables.gypi
@@ -181,7 +181,7 @@
         'skia_clang_build%': 0,
         'skia_keep_frame_pointer%': 0,
       }],
-      [ 'skia_shared_lib or skia_sanitizer or skia_os == "android" or (skia_os == "linux" and skia_angle == 1)', {
+      [ 'skia_shared_lib or skia_sanitizer or skia_os == "android" or (skia_os == "linux" and (skia_angle == 1 or skia_command_buffer == 1))', {
           'skia_pic%' : 1,
         }, {
           'skia_pic%' : 0,