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..92dba54d30d331f33b73db979afb3c210fd10b6f 100644
--- a/gpu/command_buffer/service/gles2_cmd_decoder.cc
+++ b/gpu/command_buffer/service/gles2_cmd_decoder.cc
@@ -6005,7 +6005,22 @@ 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 (enable_srgb && gl_version_info().IsAtLeastGL(4, 4)) {
+      state_.EnableDisableFramebufferSRGB(enable_srgb);

[qiankun, 2016/09/20 06:11:09]

Disable Framebuffer_SRGB if enable_srgb is false.

if (gl_version_info().IsAtLeastGL(4, 4)) {
   state_.EnableDisableFramebufferSRGB(enable_srgb);
}

[yizhou.jiang, 2016/09/20 07:00:27]

Done.

+    }
+    glGenerateMipmapEXT(target);
+  } else {

[yunchao, 2016/09/20 06:01:57]

Please add a TODO. If the target is GL_TEXTURE_3D or GL_TEXTURE_2D_ARRAY, this
change can not generate correct mipmap.

[yizhou.jiang, 2016/09/20 07:00:27]

Done.

+    state_.EnableDisableFramebufferSRGB(true);
+    if (!InitializeSRGBConverter("generateMipmap")) {
+      return;
+    }
+    srgb_converter_->SRGBGenerateMipmap(this, tex, target);
+  }
 
   if (texture_zero_level_set) {
     // This may have some unwanted side effects, but we expect command buffer