Workground for glGenerateMipmap bug in some drivers.

gpu/command_buffer/service/gles2_cmd_decoder.cc

Index: gpu/command_buffer/service/gles2_cmd_decoder.cc
diff --git a/gpu/command_buffer/service/gles2_cmd_decoder.cc b/gpu/command_buffer/service/gles2_cmd_decoder.cc
index 5444b153aa0a6c1497fd7d36f81854f63f72f591..d50db61eb3e5f0bb334c5e3b12d3bb4c562ce8cd 100644
--- a/gpu/command_buffer/service/gles2_cmd_decoder.cc
+++ b/gpu/command_buffer/service/gles2_cmd_decoder.cc
@@ -2856,7 +2856,12 @@ void GLES2DecoderImpl::DoGenerateMipmap(GLenum target) {
                "glGenerateMipmaps: Can not generate mips for npot textures");
     return;
   }
+  // Workaround for Mac driver bug. In the large scheme of things setting
+  // glTexParamter twice for glGenerateMipmap is probably not a lage performance
+  // hit so there's probably no need to make this conditional.
+  glTexParameteri(target, GL_TEXTURE_MIN_FILTER, GL_NEAREST_MIPMAP_LINEAR);
   glGenerateMipmapEXT(target);
+  glTexParameteri(target, GL_TEXTURE_MIN_FILTER, info->min_filter());
 }
 
 bool GLES2DecoderImpl::GetHelper(