Add a SafeMap equivalent to std::map but without the error-prone operator[].

Change-Id: Iae5ba2091c55a34dbd1005cf3d25fce2a8d5c1f9
diff --git a/src/compiler/codegen/MethodCodegenDriver.cc b/src/compiler/codegen/MethodCodegenDriver.cc
index 0b8a19d..dd47359 100644
--- a/src/compiler/codegen/MethodCodegenDriver.cc
+++ b/src/compiler/codegen/MethodCodegenDriver.cc
@@ -883,8 +883,7 @@
            oatGetDalvikDisassembly(cUnit, mir->dalvikInsn, "") : NULL;
         boundaryLIR = newLIR1(cUnit, kPseudoDalvikByteCodeBoundary,
                               (intptr_t) instStr);
-        cUnit->boundaryMap.insert(std::make_pair(mir->offset,
-                                 (LIR*)boundaryLIR));
+        cUnit->boundaryMap.Overwrite(mir->offset, boundaryLIR);
         /* Remember the first LIR for this block */
         if (headLIR == NULL) {
             headLIR = boundaryLIR;