Decrease call sites of currentExecutionContext()

To ensure that we're always in a correct context, I'm decreasing the call sites of currentXXX(). This CL is one of them.

BUG=357144

Review URL: https://codereview.chromium.org/293733002

git-svn-id: svn://svn.chromium.org/blink/trunk@174348 bbb929c8-8fbe-4397-9dbb-9b2b20218538