tools: implement ninja build with --build-v8-with-gn

PR-URL: #19201
Reviewed-By: Ali Ijaz Sheikh <ofrobots@google.com>
Reviewed-By: Myles Borins <myles.borins@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

common.gypi

@@ -49,7 +49,13 @@
     'conditions': [
       ['GENERATOR=="ninja"', {
         'obj_dir': '<(PRODUCT_DIR)/obj',
-        'v8_base': '<(PRODUCT_DIR)/obj/deps/v8/gypfiles/libv8_base.a',
+        'conditions': [
+          [ 'build_v8_with_gn=="true"', {
+            'v8_base': '<(PRODUCT_DIR)/obj/deps/v8/gypfiles/v8_monolith.gen/gn/obj/libv8_monolith.a',
+          }, {
+            'v8_base': '<(PRODUCT_DIR)/obj/deps/v8/gypfiles/libv8_base.a',
+          }],
+        ]
        }, {
         'obj_dir%': '<(PRODUCT_DIR)/obj.target',
         'v8_base': '<(PRODUCT_DIR)/obj.target/deps/v8/gypfiles/libv8_base.a',