[Extensions Bindings] Add a bindings/ subdirectory under renderer

extensions/renderer/bindings/DEPS

+include_rules = [
+  # The core bindings module is designed to be independent of the extensions
+  # system.
+  # TODO(devlin): We could move bindings to be a //component, if we wanted.
+  "-extensions/renderer",
+  "+extensions/renderer/bindings",
+
+  "-extensions/common",
+  # We allow a few specific includes around event filtering, since these are
+  # necessary for filtered listeners and do not themselves include any
+  # extensions system knowledge.
+  "+extensions/common/event_filter.h",
+  "+extensions/common/event_filtering_info.h",
+  "+extensions/common/event_matcher.h",
+  "+extensions/common/value_counter.h",
+]
+
+specific_include_rules = {
+  # Allow tests to include extensions system files. Typically, this shouldn't
+  # be necessary, but it can be useful.
+  ".*test\.(cc|h)$": [
+    "+extensions/renderer",
+    "+extensions/common",
+  ]
+}