[gtkmm] CssProvider::load_from_data(): Document that this throws an exception.

[Murray Cumming <murrayc src gnome org>]

commit a52118832fb03eb3ece380525f06fe9485c7cd67
Author: Murray Cumming <murrayc murrayc com>
Date:   Thu Mar 5 10:09:44 2015 +0100

    CssProvider::load_from_data(): Document that this throws an exception.

 gtk/src/cssprovider.hg |    5 ++++-
 1 files changed, 4 insertions(+), 1 deletions(-)
---
diff --git a/gtk/src/cssprovider.hg b/gtk/src/cssprovider.hg
index e217881..c982209 100644
--- a/gtk/src/cssprovider.hg
+++ b/gtk/src/cssprovider.hg
@@ -58,10 +58,13 @@ public:
 
   _WRAP_METHOD(Glib::ustring to_string() const, gtk_css_provider_to_string)
 
+  // TODO: Remove the bool return value when we can break ABI.
+  // The return value has been deprecated in the C API anyway.
   /** Loads @a data into this css provider, making it clear any previously loaded information.
    *
    * @param data CSS data loaded in memory.
-   * @result True if the data could be loaded.
+   * @result True if the data could be loaded, though an exception will always be thrown if this would 
return false.
+   * @throws CssProviderError
    */
   bool load_from_data(const std::string& data);
   _IGNORE(gtk_css_provider_load_from_data)