Bug 949875 - Delay import some WebIDL modules; r=glandium

This prevents excessive dependencies on config.status. Those extra
dependencies make WebIDL developer workflow inefficient.

--HG--
extra : rebase_source : d656410da544d4d29eb926293d8be355cd3736db

dom/bindings/mozwebidlcodegen/__init__.py

@@ -24,14 +24,8 @@ from mozbuild.util import FileAvoidWrite
 
 import mozpack.path as mozpath
 
-import WebIDL
-from Codegen import (
-    CGBindingRoot,
-    CGEventRoot,
-    CGExampleRoot,
-    GlobalGenRoots,
-)
-from Configuration import Configuration
+# There are various imports in this file in functions to avoid adding
+# dependencies to config.status. See bug 949875.
 
 
 class BuildResult(object):
@@ -300,11 +294,16 @@ class WebIDLCodegenManager(LoggingMixin):
 
     def generate_example_files(self, interface):
         """Generates example files for a given interface."""
+        from Codegen import CGExampleRoot
+
         root = CGExampleRoot(self.config, interface)
 
         return self._maybe_write_codegen(root, *self._example_paths(interface))
 
     def _parse_webidl(self):
+        import WebIDL
+        from Configuration import Configuration
+
         self.log(logging.INFO, 'webidl_parse',
             {'count': len(self._input_paths)},
             'Parsing {count} WebIDL files.')
@@ -323,6 +322,8 @@ class WebIDLCodegenManager(LoggingMixin):
         self._input_hashes = hashes
 
     def _write_global_derived(self):
+        from Codegen import GlobalGenRoots
+
         things = [('declare', f) for f in self.GLOBAL_DECLARE_FILES]
         things.extend(('define', f) for f in self.GLOBAL_DEFINE_FILES)
 
@@ -448,6 +449,11 @@ class WebIDLCodegenManager(LoggingMixin):
         return paths
 
     def _generate_build_files_for_webidl(self, filename):
+        from Codegen import (
+            CGBindingRoot,
+            CGEventRoot,
+        )
+
         self.log(logging.INFO, 'webidl_generate_build_for_input',
             {'filename': filename},
             'Generating WebIDL files derived from {filename}')