This CL fixes the debugger interface to provide correct (high-level)
information for asm.js frames.
It moves the computation of the source position from the FrameInspector
to the individual StackFrame implementations, such that we can easily
specualize it for certain frame types, and can potentially reuse this
in other locations.

Also, we are finalizing the setup of the wasm module earlier, before
executing the start function. This is required for correct stack traces
during the execution of the start function.

R=titzer@chromium.org, yangguo@chromium.org
BUG=v8:4203

Review-Url: https://codereview.chromium.org/2413693003
Cr-Commit-Position: refs/heads/master@{#40268}