[PPAPI] It is now valid to store PP_Resource 0 in a ResourceVar.

Making a resource var from PP_Resource 0 results in an empty resource
var, instead of a null var. Fixed handling of NULL Resources in
PluginResourceVar.

BUG=177017

Review URL: https://codereview.chromium.org/26273008

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@228835 0039d316-1c4b-4281-b951-d872f2087c98

diff --git a/ppapi/proxy/plugin_resource_var.cc b/ppapi/proxy/plugin_resource_var.cc
index 0ccff74..be4eec5b 100644
--- a/ppapi/proxy/plugin_resource_var.cc
+++ b/ppapi/proxy/plugin_resource_var.cc

@@ -10,7 +10,7 @@
     : resource_(resource) {}
 
 PP_Resource PluginResourceVar::GetPPResource() const {
-  return resource_->pp_resource();
+  return resource_ ? resource_->pp_resource() : 0;
 }
 
 bool PluginResourceVar::IsPending() const {

diff --git a/ppapi/proxy/plugin_resource_var.h b/ppapi/proxy/plugin_resource_var.h
index b02718b6..42be66d2 100644
--- a/ppapi/proxy/plugin_resource_var.h
+++ b/ppapi/proxy/plugin_resource_var.h

@@ -31,6 +31,7 @@
   virtual ~PluginResourceVar();
 
  private:
+  // If NULL, this represents the PP_Resource 0.
   scoped_refptr<ppapi::Resource> resource_;
 
   DISALLOW_COPY_AND_ASSIGN(PluginResourceVar);

diff --git a/ppapi/proxy/plugin_var_tracker.cc b/ppapi/proxy/plugin_var_tracker.cc
index d4ab09d..0788b99 100644
--- a/ppapi/proxy/plugin_var_tracker.cc
+++ b/ppapi/proxy/plugin_var_tracker.cc

@@ -155,8 +155,13 @@
 }
 
 ResourceVar* PluginVarTracker::MakeResourceVar(PP_Resource pp_resource) {
+  // The resource 0 returns a null resource var.
+  if (!pp_resource)
+    return new PluginResourceVar();
+
   ResourceTracker* resource_tracker = PpapiGlobals::Get()->GetResourceTracker();
   ppapi::Resource* resource = resource_tracker->GetResource(pp_resource);
+  // A non-existant resource other than 0 returns NULL.
   if (!resource)
     return NULL;
   return new PluginResourceVar(resource);

diff --git a/ppapi/shared_impl/var_tracker.h b/ppapi/shared_impl/var_tracker.h
index 379f645b..168fcb99 100644
--- a/ppapi/shared_impl/var_tracker.h
+++ b/ppapi/shared_impl/var_tracker.h

@@ -87,11 +87,17 @@
 
   // Creates a new resource var that points to a given resource ID. Returns a
   // PP_Var that references it and has an initial reference count of 1.
+  // If |pp_resource| is 0, returns a valid, empty resource var. On the plugin
+  // side (where it is possible to tell which resources exist), if |pp_resource|
+  // does not exist, returns a null var.
   PP_Var MakeResourcePPVar(PP_Resource pp_resource);
 
   // Creates a new resource var that points to a given resource ID. This is
   // implemented by the host and plugin tracker separately, because the plugin
   // keeps a reference to the resource, and the host does not.
+  // If |pp_resource| is 0, returns a valid, empty resource var. On the plugin
+  // side (where it is possible to tell which resources exist), if |pp_resource|
+  // does not exist, returns NULL.
   virtual ResourceVar* MakeResourceVar(PP_Resource pp_resource) = 0;
 
   // Return a vector containing all PP_Vars that are in the tracker. This is