LayerTreeHostImpl knows if it has an output surface.

cc/trees/layer_tree_host_impl_unittest.cc

Index: cc/trees/layer_tree_host_impl_unittest.cc
diff --git a/cc/trees/layer_tree_host_impl_unittest.cc b/cc/trees/layer_tree_host_impl_unittest.cc
index a940e3487625981d71e6fe4e14bca2f2c7701249..79501e45c69091baa1768387293c9b7926f88458 100644
--- a/cc/trees/layer_tree_host_impl_unittest.cc
+++ b/cc/trees/layer_tree_host_impl_unittest.cc
@@ -6815,5 +6815,36 @@ TEST_F(LayerTreeHostImplTest, DidBecomeActive) {
   EXPECT_EQ(1u, raw_replica_mask_layer->did_become_active_call_count());
 }
 
+class LayerTreeHostImplCountingLostSurfaces : public LayerTreeHostImplTest {
+ public:
+  LayerTreeHostImplCountingLostSurfaces() : num_lost_surfaces_(0) {}
+  virtual void DidLoseOutputSurfaceOnImplThread() OVERRIDE {
+    num_lost_surfaces_++;
+  }
+
+ protected:
+  int num_lost_surfaces_;
+};
+
+TEST_F(LayerTreeHostImplCountingLostSurfaces, TwiceLostSurface) {
+  // The medium term, we plan to remove LayerTreeHostImpl::IsContextLost().
+  // Until then, we need the state variable
+  // LayerTreeHostImpl::have_valid_output_surface_ and we can
+  // enforce the following behaviour, where calling DidLoseOutputSurface
+  // twice in a row only causes one subsequent

[danakj, 2014/08/08 13:48:49]

I think it'd be a bug if the OutputSurface called its lost callback more than
once ever, did you see this happening? I'm not sure we need to guard against
that in CC.

[dneto, 2014/08/08 14:09:12]

No, I didn't see that occur, and I haven't read any code that would cause it.  
It felt strange to make a code change without a unit test, so I tested this.  I
added the new comment to say the unit test goes beyond the required behaviour.

+  // call to LayerTreeHostImplClient::DidLoseOutputSurfaceOnImplThread().
+  // Really we just need at least one client notification each time
+  // we go from having a valid output surface to not having a valid output
+  // surface.
+  EXPECT_EQ(0, num_lost_surfaces_);
+  EXPECT_FALSE(host_impl_->IsContextLost());
+  host_impl_->DidLoseOutputSurface();
+  EXPECT_TRUE(host_impl_->IsContextLost());
+  EXPECT_EQ(1, num_lost_surfaces_);
+  host_impl_->DidLoseOutputSurface();
+  EXPECT_TRUE(host_impl_->IsContextLost());
+  EXPECT_EQ(1, num_lost_surfaces_);
+}
+
 }  // namespace
 }  // namespace cc