Add a gyp flag to allow removing dependency on ppapi.

content/browser/renderer_host/render_process_host_impl.cc

Index: content/browser/renderer_host/render_process_host_impl.cc
diff --git a/content/browser/renderer_host/render_process_host_impl.cc b/content/browser/renderer_host/render_process_host_impl.cc
index a32a14f3e91261ac5f481f4ebbdb7253164eeb46..80f8e6bc724357b7f2c5f41c5b6fa6c14e9b567d 100644
--- a/content/browser/renderer_host/render_process_host_impl.cc
+++ b/content/browser/renderer_host/render_process_host_impl.cc
@@ -567,6 +567,7 @@ void RenderProcessHostImpl::CreateMessageFilters() {
 #if defined(ENABLE_WEBRTC)
   channel_->AddFilter(new MediaStreamDispatcherHost(GetID()));
 #endif
+#if defined(ENABLE_PPAPI)
   channel_->AddFilter(
       GetContentClient()->browser()->AllowPepperPrivateFileAPI() ?
           new PepperUnsafeFileMessageFilter(
@@ -575,6 +576,7 @@ void RenderProcessHostImpl::CreateMessageFilters() {
           new PepperFileMessageFilter(GetID()));
   channel_->AddFilter(new PepperMessageFilter(PepperMessageFilter::RENDERER,
                                               GetID(), browser_context));
+#endif
 #if defined(ENABLE_INPUT_SPEECH)
   channel_->AddFilter(new InputTagSpeechDispatcherHost(
       GetID(), storage_partition_impl_->GetURLRequestContext(),