Wrap the p2p transport API in a compile time flag.

build/common.gypi

Index: build/common.gypi
diff --git a/build/common.gypi b/build/common.gypi
index 63331603b4a3e66ac413ab50e2e7ca7470774540..5fe3daaf8e6e5ad995234170e9e8babdfd722ed4 100644
--- a/build/common.gypi
+++ b/build/common.gypi
@@ -129,6 +129,9 @@
       # Remoting compilation is enabled by default. Set to 0 to disable.
       'remoting%': 1,
 
+      # Transport PPAPI is enabled by default. Set to 0 to disable.
+      'ppapi_transport%': 1,

[Sergey Ulanov, 2011/04/19 18:54:57]

It might be better to call it p2papi or p2p_apis to be consistent with the
command line flag, and because it affects not only ppapi, but will also RTC
APIs. Also please add comment saying that it must be enabled if remoting is
enabled.

+
       # If this is set, the clang plugins used on the buildbot will be used.
       # Run tools/clang/scripts/update.sh to make sure they are compiled.
       # This causes 'clang_chrome_plugins_flags' to be set.
@@ -199,6 +202,7 @@
     'use_titlecase_in_grd_files%': '<(use_titlecase_in_grd_files)',
     'use_third_party_translations%': '<(use_third_party_translations)',
     'remoting%': '<(remoting)',
+    'ppapi_transport%': '<(ppapi_transport)',
     'clang_use_chrome_plugins%': '<(clang_use_chrome_plugins)',
 
     # The release channel that this build targets. This is used to restrict
@@ -609,6 +613,9 @@
       ['remoting==1', {
         'defines': ['ENABLE_REMOTING=1'],
       }],
+      ['ppapi_transport==1', {
+        'defines': ['ENABLE_PPAPI_TRANSPORT=1'],
+      }],
       ['proprietary_codecs==1', {
         'defines': ['USE_PROPRIETARY_CODECS'],
       }],