Add a base class of Texture for interfacing with the mailbox manager.

gpu/command_buffer/service/gles2_cmd_decoder.cc

Index: gpu/command_buffer/service/gles2_cmd_decoder.cc
diff --git a/gpu/command_buffer/service/gles2_cmd_decoder.cc b/gpu/command_buffer/service/gles2_cmd_decoder.cc
index 7a0243a18d839a4f260dec14eee529a14ddd6c34..3d155d242fc2aace163adbf8cb4406c94938ce34 100644
--- a/gpu/command_buffer/service/gles2_cmd_decoder.cc
+++ b/gpu/command_buffer/service/gles2_cmd_decoder.cc
@@ -4791,7 +4791,9 @@ void GLES2DecoderImpl::TakeFrontBuffer(const Mailbox& mailbox) {
 }
 
 void GLES2DecoderImpl::ReturnFrontBuffer(const Mailbox& mailbox, bool is_lost) {
-  Texture* texture = mailbox_manager()->ConsumeTexture(mailbox);
+  TextureBase* texture_base = mailbox_manager()->ConsumeTexture(mailbox);
+  Texture* texture = texture_base ? texture_base->AsTexture() : nullptr;
+
   for (auto it = saved_back_textures_.begin(); it != saved_back_textures_.end();
        ++it) {
     if (texture != it->back_texture->texture_ref()->texture())
@@ -16051,7 +16053,10 @@ void GLES2DecoderImpl::DoConsumeTextureCHROMIUM(GLenum target,
         "glConsumeTextureCHROMIUM", "unknown texture for target");
     return;
   }
-  Texture* texture = group_->mailbox_manager()->ConsumeTexture(mailbox);
+
+  TextureBase* texture_base =
+      group_->mailbox_manager()->ConsumeTexture(mailbox);
+  Texture* texture = texture_base ? texture_base->AsTexture() : nullptr;
   if (!texture) {
     LOCAL_SET_GL_ERROR(
         GL_INVALID_OPERATION,
@@ -16111,7 +16116,9 @@ void GLES2DecoderImpl::DoCreateAndConsumeTextureINTERNAL(
         "glCreateAndConsumeTextureCHROMIUM", "client id already in use");
     return;
   }
-  Texture* texture = group_->mailbox_manager()->ConsumeTexture(mailbox);
+  TextureBase* texture_base =
+      group_->mailbox_manager()->ConsumeTexture(mailbox);
+  Texture* texture = texture_base ? texture_base->AsTexture() : nullptr;
   if (!texture) {
     EnsureTextureForClientId(target, client_id);
     LOCAL_SET_GL_ERROR(