Cleanup deoptimization code to make it architecture independent (in progress).

runtime/vm/constants_mips.h

Index: runtime/vm/constants_mips.h
===================================================================
--- runtime/vm/constants_mips.h	(revision 22382)
+++ runtime/vm/constants_mips.h	(working copy)
@@ -201,11 +201,32 @@
 const FRegister kDartLastVolatileFpuReg = F19;
 const int kDartVolatileFpuRegCount = 20;
 
+
+// TODO(regis): Move these constants to stack_frame_mips.h.
 // Dart stack frame layout.
-static const int kLastParamSlotIndex = 3;
-static const int kFirstLocalSlotIndex = -2;
+static const int kLastParamSlotIndex = 3;  // From fp.
+static const int kFirstLocalSlotIndex = -2;  // From fp.
+static const int kPcSlotIndexFromSp = -2;
 
+/* MIPS Dart Frame Layout
 
+               |                   | <- TOS
+Callee frame   | ...               |
+               | current RA        |    (PC of current frame)
+               | PC Marker         |    (callee's frame code entry)
+               +-------------------+
+Current frame  | ...               | <- SP of current frame
+               | first local       |
+               | caller's PP       |
+               | caller's FP       | <- FP of current frame
+               | caller's RA       |    (PC of caller frame)
+               | PC Marker         |    (current frame's code entry)
+               +-------------------+
+Caller frame   | last parameter    |
+               |  ...              |
+*/
+
+
 // Values for the condition field.
 // There is no condition field on MIPS, but Conditions are used and passed
 // around by the intermediate language, so we need them here, too.