Add copyright headers to remaining gyp files.

gyp/android_system.gyp

+# Copyright 2015 Google Inc.
+#
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
 # This GYP file stores the dependencies necessary to build Skia on the Android
 # platform. The OS doesn't provide many stable libraries as part of the
 # distribution so we have to build a few of them ourselves.
 #
 # We tried adding this gyp file to the android directory at the root of
 # the Skia repo, but that resulted in the generated makefiles being created
 # outside of the intended output directory. So to avoid this we created a simple
 # shim here that includes the android_system.gypi file.  The actual dependencies
 # are defined and maintained in that gypi file.
 #
 # Also this assumes that the android directory is a sibling to the directory
 # that contains your primary Skia checkout. If it is not then you must manually
 # edit the includes below to specify the actual location of the android.gypi.
 # This is due to the fact that we cannot use variables in an includes as the
 # variable expansion step for gyp happens after the includes are processed.
 {
   'includes': [
     '../platform_tools/android/gyp/skia_android.gypi',
   ],
 }