[GN] Add support for generating Xcode projects.

tools/gn/command_gen.cc

Index: tools/gn/command_gen.cc
diff --git a/tools/gn/command_gen.cc b/tools/gn/command_gen.cc
index fee3f1a31f836c7843eac42afdeb918722c43413..474e2453588fb66d06a7f382ac571a7e7e54f84a 100644
--- a/tools/gn/command_gen.cc
+++ b/tools/gn/command_gen.cc
@@ -20,6 +20,7 @@
 #include "tools/gn/switches.h"
 #include "tools/gn/target.h"
 #include "tools/gn/visual_studio_writer.h"
+#include "tools/gn/xcode_writer.h"
 
 namespace commands {
 
@@ -32,7 +33,12 @@ const char kSwitchIdeValueEclipse[] = "eclipse";
 const char kSwitchIdeValueVs[] = "vs";
 const char kSwitchIdeValueVs2013[] = "vs2013";
 const char kSwitchIdeValueVs2015[] = "vs2015";
+const char kSwitchIdeValueXcode[] = "xcode";
+const char kSwitchNinjaExtraArgs[] = "ninja-extra-args";
+const char kSwitchPattern[] = "pattern";
+const char kSwitchRootTarget[] = "root-target";
 const char kSwitchSln[] = "sln";
+const char kSwitchWorkspace[] = "workspace";
 
 // Called on worker thread to write the ninja file.
 void BackgroundDoWrite(const Target* target) {
@@ -188,6 +194,19 @@ bool RunIdeWriter(const std::string& ide,
                    "ms\n");
     }
     return res;
+  } else if (ide == kSwitchIdeValueXcode) {
+    bool res = XcodeWriter::RunAndWriteFiles(
+        command_line->GetSwitchValueNative(kSwitchWorkspace),
+        command_line->GetSwitchValueNative(kSwitchRootTarget),
+        command_line->GetSwitchValueNative(kSwitchNinjaExtraArgs),
+        command_line->GetSwitchValueNative(kSwitchPattern), build_settings,
+        builder, err);
+    if (res && !command_line->HasSwitch(switches::kQuiet)) {
+      OutputString("Generating Xcode projects took " +
+                   base::Int64ToString(timer.Elapsed().InMilliseconds()) +
+                   "ms\n");
+    }
+    return res;
   }
 
   *err = Err(Location(), "Unknown IDE: " + ide);