IDL compiler: rename GetShadowObjectTemplate => getShadowObjectTemplate

Cleanup, per request:
https://codereview.chromium.org/153403002/#msg2

TBR=haraken

Review URL: https://codereview.chromium.org/153463002

git-svn-id: svn://svn.chromium.org/blink/trunk@166381 bbb929c8-8fbe-4397-9dbb-9b2b20218538