Generate Nops to ensure that debug stack maps have distinct PC.

Change-Id: I5740ec958a20d236634b66df0e675382ed5c16fc
diff --git a/compiler/optimizing/code_generator_arm.cc b/compiler/optimizing/code_generator_arm.cc
index b32a81a..7b167e4 100644
--- a/compiler/optimizing/code_generator_arm.cc
+++ b/compiler/optimizing/code_generator_arm.cc
@@ -1679,6 +1679,10 @@
 }
 
 void InstructionCodeGeneratorARM::VisitNativeDebugInfo(HNativeDebugInfo* info) {
+  if (codegen_->HasStackMapAtCurrentPc()) {
+    // Ensure that we do not collide with the stack map of the previous instruction.
+    __ nop();
+  }
   codegen_->RecordPcInfo(info, info->GetDexPc());
 }