Add support for EXT_image_flush_external extension

ui/gl/gl_image_ozone_native_pixmap.cc

Index: ui/gl/gl_image_ozone_native_pixmap.cc
diff --git a/ui/gl/gl_image_ozone_native_pixmap.cc b/ui/gl/gl_image_ozone_native_pixmap.cc
index dd2fb3e1a4bbd9dc6f8f7fdf9d0b78af3e6bd1cb..b610dbeb1b3b7a826d5eb599b30f20fb5ce1239c 100644
--- a/ui/gl/gl_image_ozone_native_pixmap.cc
+++ b/ui/gl/gl_image_ozone_native_pixmap.cc
@@ -3,6 +3,7 @@
 // found in the LICENSE file.
 
 #include "ui/gfx/buffer_format_util.h"
+#include "ui/gl/gl_fence.h"
 #include "ui/gl/gl_image_ozone_native_pixmap.h"
 
 #define FOURCC(a, b, c, d)                                        \
@@ -242,4 +243,19 @@ unsigned GLImageOzoneNativePixmap::GetInternalFormatForTesting(
   return GL_NONE;
 }
 
+void GLImageOzoneNativePixmap::Flush() {
+  const EGLint attribs[] = {EGL_IMAGE_EXTERNAL_TARGET_NVX, EGL_DECOMPRESSED_NVX,
+                            EGL_NONE};
+
+  EGLDisplay display = eglGetDisplay(EGL_DEFAULT_DISPLAY);
+  if (!eglImageFlushExternalEXT(display, egl_image_, attribs)) {
+    LOG(ERROR) << "Failed to flush rendering";
+    return;
+  }
+
+  GLFence* fence = GLFence::Create();
+  fence->ClientWait();
+  delete fence;
+}
+
 }  // namespace gl