texture_manager: disable cubemap workaround on ES3

This workaround isn't needed in ES3 anymore because the cubemap needs
to be complete before it can be used with glReadPixels. This workaround
also used to trigger an NVIDIA bug that is now a bit more hidden.

BUG=429053
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel

Review-Url: https://codereview.chromium.org/2166083002
Cr-Commit-Position: refs/heads/master@{#406681}

content/test/gpu/gpu_tests/webgl2_conformance_expectations.py

@@ -564,10 +564,7 @@ class WebGL2ConformanceExpectations(WebGLConformanceExpectations):
         ['linux', 'opengl'], bug=483282)
 
     # Linux NVIDIA only.
-    # La la la la la la la la la la ... (well, not right now, soon)
-    self.Fail('deqp/functional/gles3/texturespecification/' +
-        'random_teximage2d_cube.html',
-        ['linux', 'nvidia'], bug=483282)
+    # La la la la la la la la la la ...
 
     # Linux NVIDIA with ANGLE only
     self.Fail('conformance/attribs/gl-disabled-vertex-attrib.html',

gpu/command_buffer/service/texture_manager.cc

@@ -2383,6 +2383,7 @@ void TextureManager::ValidateAndDoTexImage(
   // ValidateTexImage is passed already.
   Texture* texture = texture_ref->texture();
   bool need_cube_map_workaround =
+      !feature_info_->IsES3Enabled() &&
       texture->target() == GL_TEXTURE_CUBE_MAP &&
       (texture_state->force_cube_complete ||
        (texture_state->force_cube_map_positive_x_allocation &&