Add more strict DCHECKs around context state.

gpu/command_buffer/service/gl_context_virtual.cc

Index: gpu/command_buffer/service/gl_context_virtual.cc
diff --git a/gpu/command_buffer/service/gl_context_virtual.cc b/gpu/command_buffer/service/gl_context_virtual.cc
index 2582d00a754fc193d6cf1bb48e3c6aaad8217e73..51cc84fb2e969f57c75efa421067e7e032fba221 100644
--- a/gpu/command_buffer/service/gl_context_virtual.cc
+++ b/gpu/command_buffer/service/gl_context_virtual.cc
@@ -51,10 +51,12 @@ bool GLContextVirtual::IsCurrent(gl::GLSurface* surface) {
   // If it's a real surface it needs to be current.
   if (surface &&
       !surface->IsOffscreen())
-    return shared_context_->IsCurrent(surface);
+    return shared_context_->IsCurrent(surface) &&
+           shared_context_->current_virtual_context_ == this;
 
   // Otherwise, only insure the context itself is current.
-  return shared_context_->IsCurrent(NULL);
+  return shared_context_->IsCurrent(NULL) &&
+         shared_context_->current_virtual_context_ == this;

[piman, 2017/05/03 19:47:41]

One feature of this code is to avoid calling eglMakeCurrent (which is costly on
some Android devices in particular) when switching between on-screen and
offscreen contexts: since we use the same underlying GL context, if the main
framebuffer doesn't have to change (e.g. switching from on-screen to offscreen,
we don't use the main framebuffer, so whatever it is can stay).

I think this addition would defeat the purpose, because we would force
eglMakeCurrent, since IsCurrent would return false now in that case.

[Zhenyao Mo, 2017/05/03 22:21:34]

Thanks for pointing this out, although this design is confusing and could easily
be violated (like this CL) because the this function surely lets people think it
means the this virtual context is current.

Any suggestions on how we could clarify this and prevent future regression here?

 }
 
 void* GLContextVirtual::GetHandle() {