Rename gl::FenceSync to gl::Sync.

The spec refers to Sync objects, FenceSyncs being a subtype. The
motivation for this fix is to clear up the FenceSync_ entry point for
auto-generation.

BUG=angleproject:1309

Change-Id: I94c440476d701628575e7a3eea68b6dd110f41c3
Reviewed-on: https://chromium-review.googlesource.com/636516
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>
diff --git a/src/libANGLE/validationES2.cpp b/src/libANGLE/validationES2.cpp
index a997e03..88c2504 100644
--- a/src/libANGLE/validationES2.cpp
+++ b/src/libANGLE/validationES2.cpp
@@ -2251,7 +2251,7 @@
 
 static bool ValidateObjectPtrName(Context *context, const void *ptr)
 {
-    if (context->getFenceSync(reinterpret_cast<GLsync>(const_cast<void *>(ptr))) == nullptr)
+    if (context->getSync(reinterpret_cast<GLsync>(const_cast<void *>(ptr))) == nullptr)
     {
         context->handleError(InvalidValue() << "name is not a valid sync.");
         return false;