clean up gitignore; sort, add chromeos/externals, remove trailing /.

R=mtklein@google.com, epoger@google.com

Author: halcanary@google.com

Review URL: https://codereview.chromium.org/240173008

git-svn-id: http://skia.googlecode.com/svn/trunk@14249 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/.gitignore b/.gitignore
index def66f1..5f82689 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,11 +1,13 @@
 *.pyc
 *.swp
-.android_config
 .DS_Store
+.android_config
 .gclient*
-.gm-actuals/
-gyp/build/
-out
+.gm-actuals
 TAGS
-third_party/externals/
-xcodebuild/
+gyp/build
+out
+platform_tools/chromeos/third_party/externals
+platform_tools/chromeos/toolchain
+third_party/externals
+xcodebuild