Add "create_bundle" target in order to support bundle with gn.

tools/gn/toolchain.cc

Index: tools/gn/toolchain.cc
diff --git a/tools/gn/toolchain.cc b/tools/gn/toolchain.cc
index ee8e7e869ac68c077e1dedce95dd4043ccd869a7..280fb12d6f2a734e225897a15605f86e4c4c8265 100644
--- a/tools/gn/toolchain.cc
+++ b/tools/gn/toolchain.cc
@@ -24,6 +24,8 @@ const char* Toolchain::kToolSolinkModule = "solink_module";
 const char* Toolchain::kToolLink = "link";
 const char* Toolchain::kToolStamp = "stamp";
 const char* Toolchain::kToolCopy = "copy";
+const char* Toolchain::kToolCopyBundleData = "copy_bundle_data";
+const char* Toolchain::kToolCompileXCAssets = "compile_xcassets";
 
 Toolchain::Toolchain(const Settings* settings, const Label& label)
     : Item(settings, label),
@@ -56,6 +58,8 @@ Toolchain::ToolType Toolchain::ToolNameToType(const base::StringPiece& str) {
   if (str == kToolLink) return TYPE_LINK;
   if (str == kToolStamp) return TYPE_STAMP;
   if (str == kToolCopy) return TYPE_COPY;
+  if (str == kToolCopyBundleData) return TYPE_COPY_BUNDLE_DATA;
+  if (str == kToolCompileXCAssets) return TYPE_COMPILE_XCASSETS;
   return TYPE_NONE;
 }
 
@@ -74,6 +78,8 @@ std::string Toolchain::ToolTypeToName(ToolType type) {
     case TYPE_LINK: return kToolLink;
     case TYPE_STAMP: return kToolStamp;
     case TYPE_COPY: return kToolCopy;
+    case TYPE_COPY_BUNDLE_DATA: return kToolCopyBundleData;
+    case TYPE_COMPILE_XCASSETS: return kToolCompileXCAssets;
     default:
       NOTREACHED();
       return std::string();
@@ -154,6 +160,7 @@ Toolchain::ToolType Toolchain::GetToolTypeForTargetFinalOutput(
     case Target::ACTION:
     case Target::ACTION_FOREACH:
     case Target::BUNDLE_DATA:
+    case Target::CREATE_BUNDLE:
     case Target::COPY_FILES:
       return TYPE_STAMP;
     default: