Improve interpreter to interpreter invokes.

The interpreter constructs a shadow frame instead of arg array to make
interpreter to interpreter transitions faster. This adds a pointer to
an entry for the interpreter to each method.

Change-Id: If48911d3aa3470847b8548a9e92090b829f4f254
diff --git a/src/stack.h b/src/stack.h
index e2148a3..8e597b2 100644
--- a/src/stack.h
+++ b/src/stack.h
@@ -145,6 +145,11 @@
     }
   }
 
+  // Get view of vregs as range of consecutive arguments starting at i.
+  uint32_t* GetVRegArgs(size_t i) {
+    return &vregs_[i];
+  }
+
   void SetVReg(size_t i, int32_t val) {
     DCHECK_LT(i, NumberOfVRegs());
     uint32_t* vreg = &vregs_[i];