Move string-related runtime functions into separate files.

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.
 
 # TODO(jochen): These will need to be user-settable to support standalone V8
 # builds.
 v8_compress_startup_data = "off"
 v8_deprecation_warnings = false
 v8_enable_disassembler = false
 v8_enable_gdbjit = false
@@ skipping 803 matching lines @@
     "src/regexp-macro-assembler-tracer.h",
     "src/regexp-macro-assembler.cc",
     "src/regexp-macro-assembler.h",
     "src/regexp-stack.cc",
     "src/regexp-stack.h",
     "src/rewriter.cc",
     "src/rewriter.h",
     "src/runtime-profiler.cc",
     "src/runtime-profiler.h",
     "src/runtime/runtime-i18n.cc",
+    "src/runtime/runtime-json.cc",
+    "src/runtime/runtime-regexp.cc",
+    "src/runtime/runtime-strings.cc",
+    "src/runtime/runtime-uri.cc",
     "src/runtime/runtime-utils.h",
     "src/runtime/runtime.cc",
     "src/runtime/runtime.h",
+    "src/runtime/string-builder.h",
     "src/safepoint-table.cc",
     "src/safepoint-table.h",
     "src/sampler.cc",
     "src/sampler.h",
     "src/scanner-character-streams.cc",
     "src/scanner-character-streams.h",
     "src/scanner.cc",
     "src/scanner.h",
     "src/scopeinfo.cc",
     "src/scopeinfo.h",
@@ skipping 557 matching lines @@
     deps = [
       ":v8_base",
       ":v8_nosnapshot",
     ]
   }
 
   direct_dependent_configs = [ ":external_config" ]
 }
 
 }