ART: Single-frame deopt

Add deoptimization of a single frame. Works by removing the managed
code frame and jumping into the quick-to-interpreter bridge, and
the bridge understanding a stored ShadowFrame.

We need a separate fixup pass. For x86, we leave the return address
on the stack so we don't need to push it there.

Bug: 21611912
Change-Id: I06625685ced8b054244f8685ab50b238a705b9d2
diff --git a/runtime/arch/mips/context_mips.cc b/runtime/arch/mips/context_mips.cc
index bc2bf68..08ab356 100644
--- a/runtime/arch/mips/context_mips.cc
+++ b/runtime/arch/mips/context_mips.cc
@@ -30,9 +30,11 @@
   std::fill_n(fprs_, arraysize(fprs_), nullptr);
   gprs_[SP] = &sp_;
   gprs_[RA] = &ra_;
+  gprs_[A0] = &arg0_;
   // Initialize registers with easy to spot debug values.
   sp_ = MipsContext::kBadGprBase + SP;
   ra_ = MipsContext::kBadGprBase + RA;
+  arg0_ = 0;
 }
 
 void MipsContext::FillCalleeSaves(const StackVisitor& fr) {