[PPAPI] Added VarResource_Dev class.

ppapi/cpp/file_system.cc

Index: ppapi/cpp/file_system.cc
diff --git a/ppapi/cpp/file_system.cc b/ppapi/cpp/file_system.cc
index f993fdaa892459a036ff94192b5fd5460373ba08..d158d6e4c085faad1860b76119bf881508eab92e 100644
--- a/ppapi/cpp/file_system.cc
+++ b/ppapi/cpp/file_system.cc
@@ -28,6 +28,10 @@ FileSystem::FileSystem() {
 FileSystem::FileSystem(const FileSystem& other) : Resource(other) {
 }
 
+FileSystem::FileSystem(Resource resource) : Resource(resource) {
+  PP_DCHECK(ResourceIsFileSystem(resource));

[dmichael (off chromium), 2013/10/31 16:48:56]

Let's make the Resource a "Null" one in this case (for release builds). It might
make sense to add something like a "Clear" or "Release" in pp::Resource so you
can just use that here.

[Matt Giuca, 2013/10/31 23:24:43]

Done.

Note: I added Clear() as a protected method on Resource. It wouldn't hurt to
make it public, but I didn't want to change the public interface at this stage.
We can upgrade it to public later if you think that's desirable.

+}
+
 FileSystem::FileSystem(PassRef, PP_Resource resource)
     : Resource(PASS_REF, resource) {
 }
@@ -48,4 +52,12 @@ int32_t FileSystem::Open(int64_t expected_size,
       pp_resource(), expected_size, cc.pp_completion_callback());
 }
 
+// static
+bool FileSystem::ResourceIsFileSystem(const Resource& resource) {
+  if (!has_interface<PPB_FileSystem_1_0>())
+    return false;
+  return get_interface<PPB_FileSystem_1_0>()->IsFileSystem(
+      resource.pp_resource());
+}
+
 }  // namespace pp