ozone: Allow using swiftshader with --use-gl=swiftshader.

ui/ozone/platform/wayland/wayland_surface_factory.cc

Index: ui/ozone/platform/wayland/wayland_surface_factory.cc
diff --git a/ui/ozone/platform/wayland/wayland_surface_factory.cc b/ui/ozone/platform/wayland/wayland_surface_factory.cc
index 1adb2d74ace82e1fb032f9cad885e444fd3a292f..ffb0be525f964eadc2ec7b80aa133f056c66ef7a 100644
--- a/ui/ozone/platform/wayland/wayland_surface_factory.cc
+++ b/ui/ozone/platform/wayland/wayland_surface_factory.cc
@@ -141,7 +141,7 @@ class GLOzoneEGLWayland : public GLOzoneEGL {
 
  protected:
   intptr_t GetNativeDisplay() override;
-  bool LoadGLES2Bindings() override;
+  bool LoadGLES2Bindings(gl::GLImplementation impl) override;
 
  private:
   WaylandConnection* connection_;
@@ -176,9 +176,9 @@ intptr_t GLOzoneEGLWayland::GetNativeDisplay() {
   return reinterpret_cast<intptr_t>(connection_->display());
 }
 
-bool GLOzoneEGLWayland::LoadGLES2Bindings() {
+bool GLOzoneEGLWayland::LoadGLES2Bindings(gl::GLImplementation impl) {
   setenv("EGL_PLATFORM", "wayland", 0);

[rjkroege, 2017/06/12 17:23:40]

I suspect that the setenv should be skipped if we're using swiftshader. This is
a subtlety that we ought to ask tonikitoo@ about.

[tonikitoo, 2017/06/12 18:32:17]

I believe the comment pasted below is relevant (source:
https://github.com/01org/ozone-wayland/blob/master/wayland/display.cc#L167)

  // The variable EGL_PLATFORM specifies native platform to be used by the
  // drivers (atleast on Mesa). When the variable is not set, Mesa uses the
  // first platform listed in --with-egl-platforms during compilation. Thus, we
  // ensure here that wayland is set as the native platform. However, we don't
  // override the EGL_PLATFORM value in case it has already been set.

It make makes sense to me to skip setting this env variable in the case of
swiftshader use. However, I am not sure it guarantees Wayland rendering will
work (it might depend on how mesa is configured/built?).

[sadrul, 2017/06/12 19:37:00]

Sounds like the safest option is to always set the env variable here for now,
until we can confirm it's not needed for swiftshader.

-  return LoadDefaultEGLGLES2Bindings();
+  return LoadDefaultEGLGLES2Bindings(impl);
 }
 
 }  // namespace
@@ -204,8 +204,10 @@ WaylandSurfaceFactory::CreateCanvasForWidget(gfx::AcceleratedWidget widget) {
 std::vector<gl::GLImplementation>
 WaylandSurfaceFactory::GetAllowedGLImplementations() {
   std::vector<gl::GLImplementation> impls;
-  if (egl_implementation_)
+  if (egl_implementation_) {
     impls.push_back(gl::kGLImplementationEGLGLES2);
+    impls.push_back(gl::kGLImplementationSwiftShaderGL);
+  }
   impls.push_back(gl::kGLImplementationOSMesaGL);
   return impls;
 }