Add GL_NV_fence bindings to GPU process GrGLInterface setup.

This will be used by Skia for async YUV420 readbacks with ES2 ANGLE
contexts.

Bug: 1040643
Change-Id: Ifcc0bff78efcf75764902e8a2910aea7266bf327
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2015645Reviewed-by: Jonathan Backer <backer@chromium.org>
Commit-Queue: Brian Salomon <bsalomon@google.com>
Auto-Submit: Brian Salomon <bsalomon@google.com>
Cr-Commit-Position: refs/heads/master@{#734632}

ui/gl/init/create_gr_gl_interface.cc

@@ -767,6 +767,13 @@ sk_sp<GrGLInterface> CreateGrGLInterface(
     extensions.add("GL_APPLE_sync");
   }
 
+  // Skia can fall back to GL_NV_fence if GLsync objects are not available.
+  functions->fDeleteFences = gl->glDeleteFencesNVFn;
+  functions->fFinishFence = gl->glFinishFenceNVFn;
+  functions->fGenFences = gl->glGenFencesNVFn;
+  functions->fSetFence = gl->glSetFenceNVFn;
+  functions->fTestFence = gl->glTestFenceNVFn;
+
   functions->fGetInternalformativ = gl->glGetInternalformativFn;
 
   interface->fStandard = standard;