[Reland 1] Pepper takes ownership of a mailbox before passing it to the texture layer.

content/renderer/pepper/ppb_graphics_3d_impl.h

Index: content/renderer/pepper/ppb_graphics_3d_impl.h
diff --git a/content/renderer/pepper/ppb_graphics_3d_impl.h b/content/renderer/pepper/ppb_graphics_3d_impl.h
index 8216f631b7edec8232e0679c45acef71676327f3..abafd2c4b14bd0eaf87ca780c0f5e42d315e0ad9 100644
--- a/content/renderer/pepper/ppb_graphics_3d_impl.h
+++ b/content/renderer/pepper/ppb_graphics_3d_impl.h
@@ -47,6 +47,10 @@ class PPB_Graphics3D_Impl : public ppapi::PPB_Graphics3D_Shared,
   gpu::CommandBuffer::State WaitForGetOffsetInRange(int32_t start,
                                                     int32_t end) override;
   void EnsureWorkVisible() override;
+  void TakeFrontBuffer() override;
+  void ReturnFrontBuffer(const gpu::Mailbox& mailbox,
+                         const gpu::SyncToken& sync_token,
+                         bool is_lost);
 
   // Binds/unbinds the graphics of this context with the associated instance.
   // Returns true if binding/unbinding is successful.
@@ -59,11 +63,6 @@ class PPB_Graphics3D_Impl : public ppapi::PPB_Graphics3D_Shared,
   // These messages are used to send Flush callbacks to the plugin.
   void ViewInitiatedPaint();
 
-  void GetBackingMailbox(gpu::Mailbox* mailbox, gpu::SyncToken* sync_token) {
-    *mailbox = mailbox_;
-    *sync_token = sync_token_;
-  }
-
   gpu::CommandBufferProxyImpl* GetCommandBufferProxy();
 
  protected:
@@ -92,6 +91,16 @@ class PPB_Graphics3D_Impl : public ppapi::PPB_Graphics3D_Shared,
   // Notifications sent to plugin.
   void SendContextLost();
 
+  // Reuses a mailbox if one is available, otherwise makes a new one.
+  gpu::Mailbox GenerateMailbox();
+
+  // A front buffer that was recently taken from the command buffer. This should
+  // be immediately consumed by DoSwapBuffers().
+  gpu::Mailbox taken_front_buffer_;
+
+  // Mailboxes that are no longer in use.
+  std::vector<gpu::Mailbox> mailboxes_to_reuse_;
+
   // True if context is bound to instance.
   bool bound_to_instance_;
   // True when waiting for compositor to commit our backing texture.
@@ -101,8 +110,6 @@ class PPB_Graphics3D_Impl : public ppapi::PPB_Graphics3D_Shared,
   bool lost_context_ = false;
 #endif
 
-  gpu::Mailbox mailbox_;
-  gpu::SyncToken sync_token_;
   bool has_alpha_;
   std::unique_ptr<gpu::CommandBufferProxyImpl> command_buffer_;