Enables per-function far-branches for ARM and MIPS.

runtime/vm/assembler_mips.h

Index: runtime/vm/assembler_mips.h
===================================================================
--- runtime/vm/assembler_mips.h	(revision 25720)
+++ runtime/vm/assembler_mips.h	(working copy)
@@ -145,10 +145,11 @@
 
 class Assembler : public ValueObject {
  public:
-  Assembler()
+  explicit Assembler(bool use_far_branches = false)
       : buffer_(),
         object_pool_(GrowableObjectArray::Handle()),
         prologue_offset_(-1),
+        use_far_branches_(use_far_branches),
         delay_slot_available_(false),
         in_delay_slot_(false),
         comments_() { }
@@ -169,6 +170,10 @@
     buffer_.FinalizeInstructions(region);
   }
 
+  bool use_far_branches() const {
+    return FLAG_use_far_branches || use_far_branches_;
+  }
+
   // Set up a stub frame so that the stack traversal code can easily identify
   // a stub frame.
   void EnterStubFrame(bool uses_pp = false);
@@ -1094,6 +1099,7 @@
   GrowableObjectArray& object_pool_;  // Objects and patchable jump targets.
   int prologue_offset_;
 
+  const bool use_far_branches_;
   bool delay_slot_available_;
   bool in_delay_slot_;
 
@@ -1194,6 +1200,7 @@
          func << kCop1FnShift);
   }
 
+  int32_t EncodeBranchOffset(int32_t offset, int32_t instr);
 
   void EmitFarJump(int32_t offset, bool link);
   void EmitFarBranch(Opcode b, Register rs, Register rt, int32_t offset);