emulate srgb format for generateMipmap

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 8ae668f5d7615483b9a024a4df8a7122f2d5b8d8..80bb7d88767210775c3e30857ad20db99ac0a5c9 100644
--- a/gpu/command_buffer/service/gles2_cmd_decoder.cc
+++ b/gpu/command_buffer/service/gles2_cmd_decoder.cc
@@ -6005,7 +6005,28 @@ void GLES2DecoderImpl::DoGenerateMipmap(GLenum target) {
     }
   }
 
-  glGenerateMipmapEXT(target);
+  tex->GetLevelType(target, 0, &type, &internal_format);
+  bool enable_srgb =
+      GetColorEncodingFromInternalFormat(internal_format) == GL_SRGB;
+  if (!enable_srgb || !feature_info_->feature_flags().desktop_srgb_support ||
+      gl_version_info().IsAtLeastGL(4, 4)) {
+    if (gl_version_info().IsAtLeastGL(4, 4)) {
+      state_.EnableDisableFramebufferSRGB(enable_srgb);
+    }
+    glGenerateMipmapEXT(target);
+  } else {
+    if (target == GL_TEXTURE_2D) {
+      state_.EnableDisableFramebufferSRGB(true);
+      if (!InitializeSRGBConverter("generateMipmap")) {
+        return;
+      }
+      srgb_converter_->SRGBGenerateMipmap(this, tex, target);
+    } else {
+      // TODO(yizhou): If the target is GL_TEXTURE_3D or GL_TEXTURE_2D_ARRAY,
+      // this change can not generate correct mipmap.
+      glGenerateMipmapEXT(target);
+    }
+  }
 
   if (texture_zero_level_set) {
     // This may have some unwanted side effects, but we expect command buffer