This CL implements GetPossibleBreakpoints for wasm, by iterating over
all functions in the requested range and returning the location of all
instructions within that range.

The connection to the inspector will be added later, when setting
breakpoint also works for wasm: http://crrev.com/2536763002

BUG=chromium:613110
R=titzer@chromium.org

Review-Url: https://codereview.chromium.org/2588763002
Cr-Commit-Position: refs/heads/master@{#41818}