Add 'build' directory to import path of gyp_chromium.

Change https://codereview.chromium.org/1418513007/ moved a module
from tools/ to build/ causing gyp_chromium to import a different
module of the same name and breaking because the function names
are different.

BUG=

Review URL: https://codereview.chromium.org/1416223004

Cr-Commit-Position: refs/heads/master@{#356842}

build/gyp_chromium.py

@@ -40,6 +40,7 @@
 sys.path.insert(1, os.path.join(chrome_src, 'third_party', 'liblouis'))
 sys.path.insert(1, os.path.join(chrome_src, 'third_party', 'WebKit',
     'Source', 'build', 'scripts'))
+sys.path.insert(1, os.path.join(chrome_src, 'build'))
 sys.path.insert(1, os.path.join(chrome_src, 'tools'))
 sys.path.insert(1, os.path.join(chrome_src, 'tools', 'generate_shim_headers'))
 sys.path.insert(1, os.path.join(chrome_src, 'tools', 'grit'))