[turbofan] Better handling of inserted split-edge blocks

Previously, split-edge blocks inserted into CodeStubAssembler schedules
inherited the "deferredness" of their predecessor block. This tended to inline
newly inserted blocks that preceeded deferred code inline with non-deferred
code. The stack frame elider sometimes inserted stack construction into these
blocks, code which was actually was only needed in the deferred case.

This CL marks inserted split edge blocks with the deferredness of their
successors, e.g. they are defererred if their predecessor is deferrred. This
moves stack building code that logically belongs to deferred code into the
deferred code area rather than inlining it in non-deferred code.

Review-Url: https://codereview.chromium.org/2003663002
Cr-Commit-Position: refs/heads/master@{#36446}

src/compiler/schedule.cc

@@ -344,7 +344,7 @@ void Schedule::EnsureSplitEdgeForm(BasicBlock* block) {
       split_edge_block->set_control(BasicBlock::kGoto);
       split_edge_block->successors().push_back(block);
       split_edge_block->predecessors().push_back(pred);
-      split_edge_block->set_deferred(pred->deferred());
+      split_edge_block->set_deferred(block->deferred());
       *current_pred = split_edge_block;
       // Find a corresponding successor in the previous block, replace it
       // with the split edge block... but only do it once, since we only