cc: Stop using magic numbers to detect if we can use partial updates.

cc/trees/layer_tree_host.cc

Index: cc/trees/layer_tree_host.cc
diff --git a/cc/trees/layer_tree_host.cc b/cc/trees/layer_tree_host.cc
index e3a1b32924839b697d18d135ad0b816ef3711d81..34f4d2f65d29a0d4d956cef669870e988b1d6240 100644
--- a/cc/trees/layer_tree_host.cc
+++ b/cc/trees/layer_tree_host.cc
@@ -1118,6 +1118,12 @@ void LayerTreeHost::RateLimit() {
   proxy_->ForceSerializeOnSwapBuffers();
 }
 
+bool LayerTreeHost::AlwaysUsePartialTextureUpdates() {
+  if (!proxy_->GetRendererCapabilities().allow_partial_texture_updates)
+    return false;
+  return !proxy_->HasImplThread();
+}
+
 bool LayerTreeHost::RequestPartialTextureUpdate() {
   if (partial_texture_update_requests_ >= settings_.max_partial_texture_updates)
     return false;