Add back [ImplementedInBaseClass] IDL extended attribute

Originally [LegacyImplementedInBaseClass] was intended to be short-term,
as the name suggests, for some refactoring.

However, for more complex cases of 'implements' usage,
the requirements that 'implements' puts on C++ implementation
makes it an ugly mess.
Thus allowing implementation in base class seems useful long-term,
so re-introducing.

Per:
WebGLRenderingContextBase
https://codereview.chromium.org/205243013/

Documentation:
http://www.chromium.org/blink/webidl/blink-idl-extended-attributes#TOC-ImplementedInBaseClass-i-

Compare earlier CL removing this:
Remove support for [LegacyImplementedInBaseClass] IDL extended attribute 
https://codereview.chromium.org/169273002/

R=haraken
BUG=344224

Review URL: https://codereview.chromium.org/209663005

git-svn-id: svn://svn.chromium.org/blink/trunk@169830 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/bindings/IDLExtendedAttributes.txt

@@ -60,6 +60,7 @@ WillBeGarbageCollected
 GlobalContext=Window|WorkerGlobalScope|SharedWorkerGlobalScope|DedicatedWorkerGlobalScope|ServiceWorkerGlobalScope
 Immutable
 ImplementedAs=*
+ImplementedInBaseClass
 InitializedByEventConstructor
 MeasureAs=*
 NamedConstructor=*

third_party/WebKit/Source/bindings/scripts/compute_interfaces_info.py

@@ -163,7 +163,9 @@ def compute_individual_info(idl_filename):
     implemented_as = extended_attributes.get('ImplementedAs')
     # FIXME: remove [NoHeader] once switch to Python
     this_include_path = (include_path(idl_filename, implemented_as)
-                         if 'NoHeader' not in extended_attributes else None)
+                         if ('ImplementedInBaseClass' not in extended_attributes
+                             and 'NoHeader' not in extended_attributes)
+                         else None)
 
     # Handle partial interfaces
     partial_interface_name = get_partial_interface_name_from_idl(idl_file_contents)

third_party/WebKit/Source/bindings/scripts/interface_dependency_resolver.py

@@ -143,15 +143,17 @@ def transfer_extended_attributes(dependency_interface, dependency_interface_base
 
     # C++ class name of the implementation, stored in [ImplementedBy], which
     # defaults to the basename of dependency IDL file.
-    # This can be overridden by [ImplementedAs] on the dependency interface.
+    # This can be overridden by [ImplementedAs] on the dependency interface,
+    # and omitted entirely by [ImplementedInBaseClass].
     # Note that [ImplementedAs] is used with different meanings on interfaces
     # and members:
     # for Blink class name and function name (or constant name), respectively.
     # Thus we do not want to copy this from the interface to the member, but
     # instead extract it and handle it separately.
-    merged_extended_attributes['ImplementedBy'] = (
-        dependency_interface.extended_attributes.get(
-            'ImplementedAs', dependency_interface_basename))
+    if 'ImplementedInBaseClass' not in dependency_interface.extended_attributes:
+        merged_extended_attributes['ImplementedBy'] = (
+            dependency_interface.extended_attributes.get(
+                'ImplementedAs', dependency_interface_basename))
 
     for attribute in dependency_interface.attributes:
         attribute.extended_attributes.update(merged_extended_attributes)

third_party/WebKit/Source/bindings/tests/idls/TestImplements3.idl

+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+[
+    ImplementedInBaseClass, // Conflicts with default implements class name and [ImplementedAs]
+    NoInterfaceObject,
+] interface TestImplements3 {
+    attribute DOMString implements3StringAttribute;
+    static attribute DOMString implements3StaticStringAttribute;
+    void implements3VoidMethod();
+    static void implements3StaticVoidMethod();
+};

third_party/WebKit/Source/bindings/tests/idls/TestInterfacePython.idl

@@ -50,3 +50,4 @@
 
 TestInterfacePython implements TestImplements;
 TestInterfacePython implements TestImplements2;
+TestInterfacePython implements TestImplements3;