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/x86/context_x86.cc b/runtime/arch/x86/context_x86.cc
index 7096c82..987ad60 100644
--- a/runtime/arch/x86/context_x86.cc
+++ b/runtime/arch/x86/context_x86.cc
@@ -29,9 +29,11 @@
   std::fill_n(gprs_, arraysize(gprs_), nullptr);
   std::fill_n(fprs_, arraysize(fprs_), nullptr);
   gprs_[ESP] = &esp_;
+  gprs_[EAX] = &arg0_;
   // Initialize registers with easy to spot debug values.
   esp_ = X86Context::kBadGprBase + ESP;
   eip_ = X86Context::kBadGprBase + kNumberOfCpuRegisters;
+  arg0_ = 0;
 }
 
 void X86Context::FillCalleeSaves(const StackVisitor& fr) {