Wrap the p2p transport API in a compile time flag.

ppapi/ppapi_cpp.gypi

Index: ppapi/ppapi_cpp.gypi
diff --git a/ppapi/ppapi_cpp.gypi b/ppapi/ppapi_cpp.gypi
index 259fdaadc32da7700e423b16e09e107a0049fcc1..660254a2aeaee042db6d76c25b244aeb2ca886c3 100644
--- a/ppapi/ppapi_cpp.gypi
+++ b/ppapi/ppapi_cpp.gypi
@@ -69,7 +69,6 @@
         'c/dev/ppb_scrollbar_dev.h',
         'c/dev/ppb_surface_3d_dev.h',
         'c/dev/ppb_testing_dev.h',
-        'c/dev/ppb_transport_dev.h',
         'c/dev/ppb_url_util_dev.h',
         'c/dev/ppb_video_decoder_dev.h',
         'c/dev/ppb_widget_dev.h',
@@ -108,6 +107,13 @@
         'c/trusted/ppp_broker.h',
         'c/trusted/ppp_instance_trusted.h',
       ],
+      'conditions': [
+        ['ppapi_transport==1', {
+          'sources': [
+            'c/dev/ppb_transport_dev.h',
+          ],
+        }],
+      ],
     },
     {
       'target_name': 'ppapi_cpp_objects',
@@ -192,8 +198,6 @@
         'cpp/dev/selection_dev.h',
         'cpp/dev/surface_3d_dev.cc',
         'cpp/dev/surface_3d_dev.h',
-        'cpp/dev/transport_dev.cc',
-        'cpp/dev/transport_dev.h',
         'cpp/dev/url_util_dev.cc',
         'cpp/dev/url_util_dev.h',
         'cpp/dev/video_decoder_dev.cc',
@@ -229,7 +233,13 @@
           'xcode_settings': {
             'WARNING_CFLAGS': ['-Wextra', '-pedantic'],
            },
-        }]
+        }],
+        ['ppapi_transport==1', {
+          'sources': [
+            'cpp/dev/transport_dev.cc',
+            'cpp/dev/transport_dev.h',
+          ],
+        }],
       ],
     },
     {