Stop running pub get at gclient sync time and fix build bugs

.gitignore

 # commonly generated files
 *.pyc
 *.mojom.dart
 *~
 .*.sw?
 .DS_Store
 .classpath
 .cproject
 .gdb_history
 .gdbinit
@@ skipping 22 matching lines @@
 /testing/gmock/
 /testing/gtest/
 /third_party/android_tools/
 /third_party/angle/
 /third_party/appurify-python/
 /third_party/breakpad/src/
 /third_party/boringssl/src/
 /third_party/brotli/src/
 /third_party/colorama/src/
 /third_party/dart-sdk/
 /third_party/dart-pkg/archive

[tonyg, 2015/09/16 14:00:37]

This list seems hard to maintain.

It looks like the only thing we don't ignore in the dart-pkg dir is BUILD.gn. If
so, we could move that file to //build/secondary/third_party/dart-pkg/BUILD.gn.
The build system finds it there automatically and then we can just ignore this
entire dir.

[Cutch, 2015/09/16 14:18:34]

Done.

 /third_party/dart-pkg/args
+/third_party/dart-pkg/async
+/third_party/dart-pkg/barback
 /third_party/dart-pkg/box2d
 /third_party/dart-pkg/cassowary
 /third_party/dart-pkg/collection
+/third_party/dart-pkg/charcode
 /third_party/dart-pkg/crypto
+/third_party/dart-pkg/csslib
+/third_party/dart-pkg/glob
+/third_party/dart-pkg/html
+/third_party/dart-pkg/http_multi_server
+/third_party/dart-pkg/http_parser
+/third_party/dart-pkg/logging
+/third_party/dart-pkg/matcher
+/third_party/dart-pkg/mime
 /third_party/dart-pkg/newton
+/third_party/dart-pkg/package_config
 /third_party/dart-pkg/path
+/third_party/dart-pkg/plugin
+/third_party/dart-pkg/pool
+/third_party/dart-pkg/pub_semver/
 /third_party/dart-pkg/quiver
+/third_party/dart-pkg/shelf
+/third_party/dart-pkg/shelf_static
+/third_party/dart-pkg/shelf_web_socket
+/third_party/dart-pkg/source_map_stack_trace
+/third_party/dart-pkg/source_maps
 /third_party/dart-pkg/source_span
 /third_party/dart-pkg/string_scanner
+/third_party/dart-pkg/stack_trace
+/third_party/dart-pkg/test
+/third_party/dart-pkg/unittest
+/third_party/dart-pkg/utf
 /third_party/dart-pkg/vector_math
-/third_party/dart-pkg/vector_math
+/third_party/dart-pkg/watcher
 /third_party/dart-pkg/yaml
 /third_party/dejavu-fonts-ttf-2.34/ttf/*.ttf
 /third_party/freetype-android/src
 /third_party/go/
 /third_party/icu/
 /third_party/jsr-305/src/
 /third_party/libc++/trunk/
 /third_party/libc++abi/trunk/
 /third_party/libjpeg_turbo/
 /third_party/llvm/
@@ skipping 56 matching lines @@
 
 # downloaded keyboard_native resources.
 /services/keyboard_native/res/*.png
 
 # breakpad tool
 /mojo/tools/linux64/dump_syms
 /mojo/tools/linux64/symupload
 
 # downloaded prediction dictionary files.
 /services/prediction/res/*.dict