build: add option to build v8 with GN

common.gypi

@@ -48,7 +48,13 @@
         'V8_BASE': '<(PRODUCT_DIR)/obj/deps/v8/src/libv8_base.a',
        }, {
          'OBJ_DIR%': '<(PRODUCT_DIR)/obj.target',
-         'V8_BASE%': '<(PRODUCT_DIR)/obj.target/deps/v8/src/libv8_base.a',
+         'conditions': [
+           [ 'build_v8_with_gn=="true"', {
+             'V8_BASE': '<(PRODUCT_DIR)/obj.target/v8_monolith/geni/gn/obj/libv8_monolith.a',
+           }, {
+             'V8_BASE': '<(PRODUCT_DIR)/obj.target/deps/v8/src/libv8_base.a',
+           }],
+         ],
       }],
       ['OS == "win"', {
         'os_posix': 0,

configure

@@ -55,6 +55,10 @@ sys.path.insert(0, 'tools')
 import getmoduleversion
 from gyp_node import run_gyp
 
+# imports in deps/v8/tools/node
+sys.path.insert(0, os.path.join('deps', 'v8', 'tools', 'node'))
+from fetch_deps import FetchDeps
+
 # parse our options
 parser = optparse.OptionParser()
 
@@ -548,6 +552,12 @@ parser.add_option('--without-bundled-v8',
     help='do not use V8 includes from the bundled deps folder. ' +
          '(This mode is not officially supported for regular applications)')
 
+parser.add_option('--build-v8-with-gn',
+    action='store_true',
+    dest='build_v8_with_gn',
+    default=False,
+    help='build V8 using GN instead of gyp')
+
 # Create compile_commands.json in out/Debug and out/Release.
 parser.add_option('-C',
     action='store_true',
@@ -1027,6 +1037,7 @@ def configure_v8(o):
   o['variables']['v8_trace_maps'] = 1 if options.trace_maps else 0
   o['variables']['node_use_v8_platform'] = b(not options.without_v8_platform)
   o['variables']['node_use_bundled_v8'] = b(not options.without_bundled_v8)
+  o['variables']['build_v8_with_gn'] = b(options.build_v8_with_gn)
   o['variables']['force_dynamic_crt'] = 1 if options.shared else 0
   o['variables']['node_enable_d8'] = b(options.enable_d8)
   # Unconditionally force typed arrays to allocate outside the v8 heap. This
@@ -1037,6 +1048,13 @@ def configure_v8(o):
     o['variables']['test_isolation_mode'] = 'noop'  # Needed by d8.gyp.
   if options.without_bundled_v8 and options.enable_d8:
     raise Exception('--enable-d8 is incompatible with --without-bundled-v8.')
+  if options.without_bundled_v8 and options.build_v8_with_gn:
+    raise Exception(
+        '--build-v8-with-gn is incompatible with --without-bundled-v8.')
+  if options.build_v8_with_gn:
+    v8_path = os.path.join('deps', 'v8')
+    print('Fetching dependencies to build V8 with GN')
+    FetchDeps(v8_path)
 
 
 def configure_openssl(o):

node.gypi

@@ -17,9 +17,15 @@
     }],
     [ 'node_use_bundled_v8=="true"', {
       'dependencies': [
-        'deps/v8/src/v8.gyp:v8',
         'deps/v8/src/v8.gyp:v8_libplatform'
       ],
+      'conditions': [
+        [ 'build_v8_with_gn=="true"', {
+          'dependencies': ['deps/v8/src/v8.gyp:v8_monolith'],
+        }, {
+          'dependencies': ['deps/v8/src/v8.gyp:v8'],
+        }],
+      ],
     }],
     [ 'node_use_v8_platform=="true"', {
       'defines': [