Add control of manual mipmapping to GrContextOptions

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2054623003

Review-Url: https://codereview.chromium.org/2054623003

include/gpu/GrContextOptions.h

@@ -67,6 +67,11 @@ struct GrContextOptions {
     /** Force us to do all swizzling manually in the shader and don't rely on extensions to do
         swizzling. */
     bool fUseShaderSwizzling;
+
+    /** Construct mipmaps manually, via repeated downsampling draw-calls. This is used when
+        the driver's implementation (glGenerateMipmap) contains bugs. This requires mipmap
+        level and LOD control (ie desktop or ES3). */
+    bool fDoManualMipmapping;
 };
 
 #endif

src/gpu/gl/GrGLCaps.cpp

@@ -551,7 +551,8 @@ void GrGLCaps::init(const GrContextOptions& contextOptions,
     // glGenerateMipmap. Our implementation requires mip-level sampling control. Additionally,
     // it can be much slower (especially on mobile GPUs), so we opt-in only when necessary:
     if (fMipMapLevelAndLodControlSupport &&
-        ((kIntel_GrGLVendor == ctxInfo.vendor()) ||
+        (contextOptions.fDoManualMipmapping ||
+         (kIntel_GrGLVendor == ctxInfo.vendor()) ||
          (kNVIDIA_GrGLDriver == ctxInfo.driver() && isMAC) ||
          (kATI_GrGLVendor == ctxInfo.vendor()))) {
         fDoManualMipmapping = true;