Add a caps bit to enable/disable the new manual mip-mapper

src/gpu/gl/GrGLGpu.cpp

Index: src/gpu/gl/GrGLGpu.cpp
diff --git a/src/gpu/gl/GrGLGpu.cpp b/src/gpu/gl/GrGLGpu.cpp
index 1744e2503636db460b2e1254c7ebe371cbef5199..fe32556823d6208250f9cb5efbb0e31f9d59f70a 100644
--- a/src/gpu/gl/GrGLGpu.cpp
+++ b/src/gpu/gl/GrGLGpu.cpp
@@ -4314,14 +4314,12 @@ bool GrGLGpu::copySurfaceAsBlitFramebuffer(GrSurface* dst,
     return true;
 }
 
-bool gManualMipmaps = true;
-
 // Manual implementation of mipmap generation, to work around driver bugs w/sRGB.
 // Uses draw calls to do a series of downsample operations to successive mips.
 // If this returns false, then the calling code falls back to using glGenerateMipmap.
 bool GrGLGpu::generateMipmap(GrGLTexture* texture, bool gammaCorrect) {
-    // Global switch for manual mipmap generation:
-    if (!gManualMipmaps) {
+    // Our iterative downsample requires the ability to limit which level we're sampling:
+    if (!this->glCaps().doManualMipmapping()) {
         return false;
     }
 
@@ -4335,11 +4333,6 @@ bool GrGLGpu::generateMipmap(GrGLTexture* texture, bool gammaCorrect) {
         return false;
     }
 
-    // Our iterative downsample requires the ability to limit which level we're sampling:
-    if (!this->glCaps().mipMapLevelAndLodControlSupport()) {
-        return false;
-    }
-
     // If we're mipping an sRGB texture, we need to ensure FB sRGB is correct:
     if (GrPixelConfigIsSRGB(texture->config())) {
         // If we have write-control, just set the state that we want: