Bug 1621836 - Make SurfaceTextureHost::NumSubTextures() returns 0 when SurfaceTexture does not exist r=nical

When NumSubTextures() returns 0, SurfaceTextureHost is not rendered to WebRebder by a check of AsyncImagePipelineManager::UpdateImageKeys().

Differential Revision: https://phabricator.services.mozilla.com/D66514

--HG--
extra : moz-landing-system : lando

gfx/layers/opengl/TextureHostOGL.cpp

@@ -646,6 +646,8 @@ void SurfaceTextureHost::CreateRenderTexture(
                                                  texture.forget());
 }
 
+uint32_t SurfaceTextureHost::NumSubTextures() { return mSurfTex ? 1 : 0; }
+
 void SurfaceTextureHost::PushResourceUpdates(
     wr::TransactionBuilder& aResources, ResourceUpdateOp aOp,
     const Range<wr::ImageKey>& aImageKeys, const wr::ExternalImageId& aExtID) {

gfx/layers/opengl/TextureHostOGL.h

@@ -430,6 +430,8 @@ class SurfaceTextureHost : public TextureHost {
   void CreateRenderTexture(
       const wr::ExternalImageId& aExternalImageId) override;
 
+  uint32_t NumSubTextures() override;
+
   void PushResourceUpdates(wr::TransactionBuilder& aResources,
                            ResourceUpdateOp aOp,
                            const Range<wr::ImageKey>& aImageKeys,