Revert "Revert "Avoid checking extension string in GrGLGpu::onResetContext.""

This reverts commit 04c1cccaa45e8a96fcc82f027435b50093b935ea.

Reland that preserves GL_NV_shader_framebuffer_fetch support.

Change-Id: I8d51321a552d0abfd0a8fa36c4d00b9b0e0d8663
Reviewed-on: https://skia-review.googlesource.com/c/187300
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
4 files changed