[build] Introduce an embedder version string

BUILD.gn

 # 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.
 
 import("//build/config/android/config.gni")
 import("//build/config/arm.gni")
 import("//build/config/dcheck_always_on.gni")
 import("//build/config/mips.gni")
 import("//build/config/sanitizers/sanitizers.gni")
 
@@ skipping 11 matching lines @@
 
   # Sets -DVERIFY_HEAP.
   v8_enable_verify_heap = false
 
   # Sets -DVERIFY_PREDICTABLE
   v8_enable_verify_predictable = false
 
   # Enable compiler warnings when using V8_DEPRECATED apis.
   v8_deprecation_warnings = false
 
+  # Allow the embedder to add a custom suffix to the version string.
+  v8_embedder_string = ""
+
   # Enable compiler warnings when using V8_DEPRECATE_SOON apis.
   v8_imminent_deprecation_warnings = ""
 
   # Embeds the given script into the snapshot.
   v8_embed_script = ""
 
   # Sets -dENABLE_DISASSEMBLER.
   v8_enable_disassembler = ""
 
   # Sets -dENABLE_GDB_JIT_INTERFACE.
@@ skipping 125 matching lines @@
   if (v8_use_external_startup_data) {
     defines = [ "V8_USE_EXTERNAL_STARTUP_DATA" ]
   }
 }
 
 config("features") {
   visibility = [ ":*" ]  # Only targets in this file can depend on this.
 
   defines = []
 
+  if (v8_embedder_string != "") {
+    defines += [ "V8_EMBEDDER_STRING=\"$v8_embedder_string\"" ]
+  }
+
   if (v8_enable_disassembler) {
     defines += [ "ENABLE_DISASSEMBLER" ]
   }
   if (v8_enable_gdbjit) {
     defines += [ "ENABLE_GDB_JIT_INTERFACE" ]
   }
   if (v8_object_print) {
     defines += [ "OBJECT_PRINT" ]
   }
   if (v8_enable_verify_heap) {
@@ skipping 2825 matching lines @@
   ]
 
   configs = [
     ":external_config",
     ":internal_config_base",
   ]
 }
 
 v8_fuzzer("wasm_data_section_fuzzer") {
 }