Call IGL method to flush Metal texture cache

Summary: This diff updates two places were accessing the texture cache held in an IGL Metal PlatformDevice and attempting to flush it without checking if it is null first. The update is to call the existing method on the PlatformDevice that does the same thing but includes the null check.

Reviewed By: syeh1

Differential Revision: D49151276

fbshipit-source-id: b12a846d7cc917affc8ff06b4e39629437b5b12f

src/igl/metal/PlatformDevice.h

@@ -105,7 +105,7 @@ class PlatformDevice final : public IPlatformDevice {
   /// @return An accurate pixel format that is suitable for rendering or invalid if failed.
   TextureFormat getNativeDrawableTextureFormat(CALayer* nativeDrawable, Result* outResult);
 
-  void flushNativeTextureCache();
+  void flushNativeTextureCache() const;
 
   CVMetalTextureCacheRef getTextureCache();
 

src/igl/metal/PlatformDevice.mm

@@ -242,7 +242,7 @@
   return textureCache_;
 }
 
-void PlatformDevice::flushNativeTextureCache() {
+void PlatformDevice::flushNativeTextureCache() const {
 #if (!TARGET_OS_SIMULATOR || __IPHONE_OS_VERSION_MAX_ALLOWED >= 130000)
   if (textureCache_) {
     CVMetalTextureCacheFlush(textureCache_, 0);