Add more strict DCHECKs around context state.

gpu/command_buffer/service/gl_context_virtual.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "gpu/command_buffer/service/gl_context_virtual.h"
 
 #include "base/callback.h"
 #include "gpu/command_buffer/service/gl_state_restorer_impl.h"
 #include "gpu/command_buffer/service/gles2_cmd_decoder.h"
 #include "ui/gl/gl_gl_api_implementation.h"
@@ skipping 33 matching lines @@
   if (IsCurrent(surface)) {
     shared_context_->OnReleaseVirtuallyCurrent(this);
     shared_context_->ReleaseCurrent(surface);
   }
 }
 
 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() {
   return shared_context_->GetHandle();
 }
 
 scoped_refptr<gl::GPUTimingClient> GLContextVirtual::CreateGPUTimingClient() {
   return shared_context_->CreateGPUTimingClient();
 }
 
@@ skipping 30 matching lines @@
 
 gl::YUVToRGBConverter* GLContextVirtual::GetYUVToRGBConverter() {
   return shared_context_->GetYUVToRGBConverter();
 }
 
 GLContextVirtual::~GLContextVirtual() {
   Destroy();
 }
 
 }  // namespace gpu