Fix BindGroupLayout leak in PipelineLayout default.

PipelineLayout was re-entering in NXT to create the default empty BGLs,
but forgot to remove the initial external refcount for them.

Fixing this showed an issue where it was impossible to externally
reference a RefCounted that had only internal references, fix this as
well and add a test.

src/backend/PipelineLayout.cpp

@@ -60,6 +60,8 @@ namespace backend {
         for (size_t group = 0; group < kMaxBindGroups; ++group) {
             if (!mBindGroupLayouts[group]) {
                 mBindGroupLayouts[group] = mDevice->CreateBindGroupLayoutBuilder()->GetResult();
+                // Remove the external ref objects are created with
+                mBindGroupLayouts[group]->Release();
             }
         }
 

src/backend/RefCounted.cpp

@@ -26,13 +26,16 @@ namespace backend {
 
     void RefCounted::ReferenceInternal() {
         ASSERT(mInternalRefs != 0);
+
         // TODO(cwallez@chromium.org): what to do on overflow?
         mInternalRefs++;
     }
 
     void RefCounted::ReleaseInternal() {
         ASSERT(mInternalRefs != 0);
+
         mInternalRefs--;
+
         if (mInternalRefs == 0) {
             ASSERT(mExternalRefs == 0);
             // TODO(cwallez@chromium.org): would this work with custom allocators?
@@ -49,14 +52,23 @@ namespace backend {
     }
 
     void RefCounted::Reference() {
-        ASSERT(mExternalRefs != 0);
+        ASSERT(mInternalRefs != 0);
+
+        // mExternalRefs != 0 counts as one internal ref.
+        if (mExternalRefs == 0) {
+            ReferenceInternal();
+        }
+
         // TODO(cwallez@chromium.org): what to do on overflow?
         mExternalRefs++;
     }
 
     void RefCounted::Release() {
+        ASSERT(mInternalRefs != 0);
         ASSERT(mExternalRefs != 0);
+
         mExternalRefs--;
+        // mExternalRefs != 0 counts as one internal ref.
         if (mExternalRefs == 0) {
             ReleaseInternal();
         }