Mojo JS bindings: flip the default value of use_new_js_bindings to true.

BUG=699569
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.android:android_optional_gpu_tests_rel;master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel

Review-Url: https://codereview.chromium.org/2910703004
Cr-Commit-Position: refs/heads/master@{#475327}
28 files changed