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

tools/gn/target.cc

Index: tools/gn/target.cc
diff --git a/tools/gn/target.cc b/tools/gn/target.cc
index 9435d47ac59bfce8453c1e8216455f77f4cd27c2..714fd911f9657c038dda56c1b096ded0365d759c 100644
--- a/tools/gn/target.cc
+++ b/tools/gn/target.cc
@@ -224,6 +224,8 @@ const char* Target::GetStringForOutputType(OutputType type) {
       return "ActionForEach";
     case BUNDLE_DATA:
       return "Bundle data";
+    case CREATE_BUNDLE:
+      return "Create bundle";
     default:
       return "";
   }
@@ -277,6 +279,7 @@ bool Target::OnResolved(Err* err) {
     all_libs_.append(cur.libs().begin(), cur.libs().end());
   }
 
+  PullRecursiveBundleData();
   PullDependentTargetLibs();
   PullRecursiveHardDeps();
   if (!ResolvePrecompiledHeaders(err))
@@ -318,6 +321,7 @@ bool Target::IsFinal() const {
          output_type_ == ACTION ||
          output_type_ == ACTION_FOREACH ||
          output_type_ == COPY_FILES ||
+         output_type_ == CREATE_BUNDLE ||
          (output_type_ == STATIC_LIBRARY && complete_static_lib_);
 }
 
@@ -476,12 +480,48 @@ void Target::PullRecursiveHardDeps() {
   }
 }
 
+void Target::PullRecursiveBundleData() {
+  if (output_type_ != CREATE_BUNDLE)
+    return;
+
+  std::set<const Target*> visited;
+  std::vector<const Target*> deps;
+  deps.push_back(this);
+
+  while (!deps.empty()) {
+    const Target* current = deps.back();
+    deps.pop_back();
+
+    if (visited.find(current) != visited.end())
+      continue;
+    visited.insert(current);
+
+    if (current->output_type_ == BUNDLE_DATA)
+      bundle_data_.AddFileRuleFromTarget(current);
+
+    for (const LabelTargetPair& pair : current->GetDeps(DEPS_ALL)) {
+      DCHECK(pair.ptr);
+      DCHECK(pair.ptr->toolchain_);
+      if (visited.find(pair.ptr) != visited.end())
+        continue;
+
+      if (pair.ptr->output_type() == CREATE_BUNDLE)
+        continue;
+
+      deps.push_back(pair.ptr);
+    }
+  }
+
+  bundle_data_.GetSourceFiles(&sources_);
+}
+
 void Target::FillOutputFiles() {
   const Tool* tool = toolchain_->GetToolForTargetFinalOutput(this);
   bool check_tool_outputs = false;
   switch (output_type_) {
     case GROUP:
     case BUNDLE_DATA:
+    case CREATE_BUNDLE:
     case SOURCE_SET:
     case COPY_FILES:
     case ACTION:
@@ -547,6 +587,10 @@ void Target::FillOutputFiles() {
       NOTREACHED();
   }
 
+  // Count anything generated from bundle_data dependencies.
+  if (output_type_ == CREATE_BUNDLE)
+    bundle_data_.GetOutputFiles(settings(), &computed_outputs_);
+
   // Count all outputs from this tool as something generated by this target.
   if (check_tool_outputs) {
     SubstitutionWriter::ApplyListToLinkerAsOutputFile(