bind-gen: Implement/improve blink_api_call to support optional args

Implements support of optional arguments.

Bug: 839389
Change-Id: I1e35774a52fc18786eb712b2dcc6d9456faea5d8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1942895Reviewed-by: Hitoshi Yoshida <peria@chromium.org>
Commit-Queue: Yuki Shiino <yukishiino@chromium.org>
Cr-Commit-Position: refs/heads/master@{#720831}

third_party/blink/renderer/bindings/scripts/bind_gen/blink_v8_bridge.py

@@ -100,6 +100,7 @@ def blink_type_info(idl_type):
             blink_impl_type,
             member_fmt="Member<{}>",
             ref_fmt="{}*",
+            value_fmt="{}*",
             is_nullable=True)
 
     if (real_type.is_sequence or real_type.is_frozen_array
@@ -168,13 +169,18 @@ def native_value_tag(idl_type):
         return "IDLNullable<{}>".format(native_value_tag(real_type.inner_type))
 
 
-def make_v8_to_blink_value(blink_var_name, v8_value_expr, idl_type):
+def make_v8_to_blink_value(blink_var_name,
+                           v8_value_expr,
+                           idl_type,
+                           default_value=None):
     """
     Returns a SymbolNode whose definition converts a v8::Value to a Blink value.
     """
     assert isinstance(blink_var_name, str)
     assert isinstance(v8_value_expr, str)
     assert isinstance(idl_type, web_idl.IdlType)
+    assert (default_value is None
+            or isinstance(default_value, web_idl.LiteralConstant))
 
     pattern = (
         "const auto& ${{{_1}}} = NativeValueTraits<{_2}>::NativeValue({_3});")

third_party/blink/renderer/bindings/scripts/web_idl/__init__.py

@@ -47,6 +47,7 @@ from .function_like import FunctionLike
 from .function_like import OverloadGroup
 from .idl_type import IdlType
 from .interface import Interface
+from .literal_constant import LiteralConstant
 from .namespace import Namespace
 from .operation import Operation
 from .operation import OperationGroup