Make javac.py assume UTF-8 encoding always

My understanding is that by-default javac
pulls encoding from the user's environment
http://stackoverflow.com/questions/9661935/how-to-change-the-defaults-system-java-encode-form-in-windows
http://stackoverflow.com/questions/11343828/file-encoding-has-no-effect-lc-all-environment-variable-does-it
which is wrong for Chromium where all of our
source files are known to be UTF-8, regardless
of what the user has set in their environment.

In my case I was using Chrome Remote Desktop
to connect to my linux machine and for
whatever reason LANG was missing from the
resulting environment.  After this patch
mojo_shell builds correctly for Android again.

BUG=419378

Review URL: https://codereview.chromium.org/869673002

Cr-Commit-Position: refs/heads/master@{#313432}

build/android/gyp/javac.py

@@ -72,6 +72,9 @@ def DoJavac(
 
   javac_args = [
       '-g',
+      # Chromium only allows UTF8 source files.  Being explicit avoids
+      # javac pulling a default encoding from the user's environment.
+      '-encoding', 'UTF-8',
       '-source', '1.7',
       '-target', '1.7',
       '-classpath', ':'.join(classpath),