content: Port layout_test_helper target to GN build.

This is necessary because it is one of the dependencies of the
'blink_tests' group that should be built.

BUG=483171
R=avi@chromium.org,dpranke@chromium.org

Review URL: https://codereview.chromium.org/1131773004

Cr-Commit-Position: refs/heads/master@{#329580}

BUILD.gn

@@ -752,8 +752,8 @@ if (!is_ios) {
 
     if (is_win) {
       deps += [
+        "//content/shell:layout_test_helper",
         #'../content/content_shell_and_tests.gyp:content_shell_crash_service', TODO(GYP)
-        #'../content/content_shell_and_tests.gyp:layout_test_helper', TODO(GYP)
       ]
     }
 
@@ -764,7 +764,7 @@ if (!is_ios) {
     if (is_mac) {
       deps += [
         "//breakpad:dump_syms($host_toolchain)",
-        #'../content/content_shell_and_tests.gyp:layout_test_helper', TODO(GYP)
+        "//content/shell:layout_test_helper",
       ]
     }
 

content/content_shell.gypi

@@ -797,6 +797,7 @@
     ['OS=="mac" or OS=="win"', {
       'targets': [
         {
+          # GN version: //content/shell:layout_test_helper
           'target_name': 'layout_test_helper',
           'type': 'executable',
           'sources': [

content/shell/BUILD.gn

@@ -541,3 +541,17 @@ if (!is_android && !is_mac) {
     ]
   }
 }
+
+if (is_mac || is_win) {
+  # GYP version: content/content_shell_and_tests.gyp:layout_test_helper
+  executable("layout_test_helper") {
+    sources = [
+      "renderer/test_runner/helper/layout_test_helper_mac.mm",
+      "renderer/test_runner/helper/layout_test_helper_win.cc",
+    ]
+
+    if (is_mac) {
+      libs = [ "AppKit.framework" ]
+    }
+  }
+}