Add remoting and PPAPI tests to GN build

ppapi/ppapi_tests.gypi

Index: ppapi/ppapi_tests.gypi
diff --git a/ppapi/ppapi_tests.gypi b/ppapi/ppapi_tests.gypi
index 562903d5c0b8a9e2181e8f61cb79bf15b16cc823..ee4fd5461d557a32a5870d89f62960d913933c2e 100644
--- a/ppapi/ppapi_tests.gypi
+++ b/ppapi/ppapi_tests.gypi
@@ -5,6 +5,7 @@
 {
   'targets': [
     {
+      # GN version: //ppapi:ppapi_tests
       'target_name': 'ppapi_tests',
       'type': 'loadable_module',
       'include_dirs': [
@@ -106,6 +107,7 @@
     },
 
     {
+      # GN version: //ppapi:ppapi_perftests
       'target_name': 'ppapi_perftests',
       'type': 'executable',
       'variables': {
@@ -132,6 +134,7 @@
       ],
     },
     {
+      # GN version: //ppapi:ppapi_unittests
       'target_name': 'ppapi_unittests',
       'type': 'executable',
       'variables': {
@@ -153,6 +156,7 @@
         '../ui/surface/surface.gyp:surface',
       ],
       'sources': [
+        # Note: sources list duplicated in GN build.
         'host/resource_message_filter_unittest.cc',
         'proxy/device_enumeration_resource_helper_unittest.cc',
         'proxy/file_chooser_resource_unittest.cc',