Move startup_helper_win.cc to separate target for incremental build

content/content_app.gypi

Index: content/content_app.gypi
diff --git a/content/content_app.gypi b/content/content_app.gypi
index 0684e41d46114397dd098a85fdf2479229b5b8be..00ee842b1483168c88dc59d9cb033df06ef51c17 100644
--- a/content/content_app.gypi
+++ b/content/content_app.gypi
@@ -26,13 +26,11 @@
     'app/content_main_runner.cc',
     'app/mojo/mojo_init.cc',
     'app/mojo/mojo_init.h',
-    'app/startup_helper_win.cc',
     'public/app/android_library_loader_hooks.h',
     'public/app/content_main.h',
     'public/app/content_main_delegate.cc',
     'public/app/content_main_delegate.h',
     'public/app/content_main_runner.h',
-    'public/app/startup_helper_win.h',
   ],
   'conditions': [
     ['((OS=="linux" and os_posix==1 and use_aura==1) or OS=="android") and use_allocator!="none"', {
@@ -41,11 +39,6 @@
         '../base/allocator/allocator.gyp:allocator',
       ],
     }],
-    ['OS=="win"', {
-      'dependencies': [
-        '../sandbox/sandbox.gyp:sandbox',
-      ],
-    }],
     ['OS=="android"', {
       'sources!': [
         'app/content_main.cc',
@@ -58,6 +51,11 @@
         '../build/android/cpufeatures.gypi',
       ],
     }],
+    ['OS=="win"', {
+      'dependencies': [
+        'content_startup_helper_win',
+      ],
+    }],
     ['OS=="ios"', {
       'sources!': [
         'app/content_main.cc',