VM: [DBC] Fix GetDeoptFpOffset in the presence of materializations.
VM: [DBC] Fix GetDeoptFpOffset in the presence of materializations.

Number of materializations was not taken into account when computing FP offset
on DBC.

This fixes flaky crashes on language/vm/optimized_stacktrace_test.

R=zra@google.com, rmacnak@google.com
BUG=

Review-Url: https://codereview.chromium.org/2571843002 .

dart-lang/sdk,dartino/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dart-lang/sdk,dart-lang/sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dart-lang/sdk,dartino/dart-sdk,dartino/dart-sdk,dartino/dart-sdk,dartino/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk,dartino/dart-sdk,dart-archive/dart-sdk,dart-lang/sdk,dart-lang/sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dartino/dart-sdk