MIPS: Add flag for testing long branch mode.

src/mips/assembler-mips.cc

Index: src/mips/assembler-mips.cc
diff --git a/src/mips/assembler-mips.cc b/src/mips/assembler-mips.cc
index f551dd5e104129e910996606ce45cc0c47573146..9adb9001fa400df8397a29eac072279f25a6db69 100644
--- a/src/mips/assembler-mips.cc
+++ b/src/mips/assembler-mips.cc
@@ -313,11 +313,12 @@ Assembler::Assembler(Isolate* isolate, void* buffer, int buffer_size)
   trampoline_pool_blocked_nesting_ = 0;
   // We leave space (16 * kTrampolineSlotsSize)
   // for BlockTrampolinePoolScope buffer.
-  next_buffer_check_ = kMaxBranchOffset - kTrampolineSlotsSize * 16;
+  next_buffer_check_ = FLAG_force_long_branches
+      ? kMaxInt : kMaxBranchOffset - kTrampolineSlotsSize * 16;
   internal_trampoline_exception_ = false;
   last_bound_pos_ = 0;
 
-  trampoline_emitted_ = false;
+  trampoline_emitted_ = FLAG_force_long_branches;
   unbound_labels_count_ = 0;
   block_buffer_growth_ = false;