Adds support for debugger API on MIPS.

runtime/vm/assembler_mips.cc

Index: runtime/vm/assembler_mips.cc
===================================================================
--- runtime/vm/assembler_mips.cc	(revision 21950)
+++ runtime/vm/assembler_mips.cc	(working copy)
@@ -331,9 +331,9 @@
     addiu(SP, SP, Immediate(-4 * kWordSize));
     sw(ZR, Address(SP, 3 * kWordSize));  // PC marker is 0 in stubs.
     sw(RA, Address(SP, 2 * kWordSize));
-    sw(PP, Address(SP, 1 * kWordSize));
-    sw(FP, Address(SP, 0 * kWordSize));
-    mov(FP, SP);
+    sw(FP, Address(SP, 1 * kWordSize));
+    sw(PP, Address(SP, 0 * kWordSize));
+    addiu(FP, SP, Immediate(1 * kWordSize));
     // Setup pool pointer for this stub.
     Label next;
     bal(&next);
@@ -356,13 +356,14 @@
 
 
 void Assembler::LeaveStubFrame(bool uses_pp) {
-  mov(SP, FP);
   if (uses_pp) {
+    addiu(SP, FP, Immediate(-1 * kWordSize));
     lw(RA, Address(SP, 2 * kWordSize));
-    lw(PP, Address(SP, 1 * kWordSize));
-    lw(FP, Address(SP, 0 * kWordSize));
+    lw(FP, Address(SP, 1 * kWordSize));
+    lw(PP, Address(SP, 0 * kWordSize));
     addiu(SP, SP, Immediate(4 * kWordSize));
   } else {
+    mov(SP, FP);
     lw(RA, Address(SP, 1 * kWordSize));
     lw(FP, Address(SP, 0 * kWordSize));
     addiu(SP, SP, Immediate(3 * kWordSize));
@@ -449,6 +450,8 @@
       2 * kWordSize +  // FP and RA.
       kDartVolatileFpuRegCount * kWordSize;
 
+  TraceSimMsg("EnterCallRuntimeFrame");
+
   if (prologue_offset_ == -1) {
     prologue_offset_ = CodeSize();
   }
@@ -491,6 +494,8 @@
       2 * kWordSize +  // FP and RA.
       kDartVolatileFpuRegCount * kWordSize;
 
+  TraceSimMsg("LeaveCallRuntimeFrame");
+
   // SP might have been modified to reserve space for arguments
   // and ensure proper alignment of the stack frame.
   // We need to restore it before restoring registers.