Improve type propagation with if-contexts

This works by adding a new instruction (HBoundType) after each `if (a
instanceof ClassA) {}` to bound the type that `a` can take in the True-
dominated blocks.

Change-Id: Iae6a150b353486d4509b0d9b092164675732b90c
diff --git a/compiler/optimizing/code_generator_x86.cc b/compiler/optimizing/code_generator_x86.cc
index 8a73eb4..e151c6b 100644
--- a/compiler/optimizing/code_generator_x86.cc
+++ b/compiler/optimizing/code_generator_x86.cc
@@ -3914,5 +3914,17 @@
   }
 }
 
+void LocationsBuilderX86::VisitBoundType(HBoundType* instruction) {
+  // Nothing to do, this should be removed during prepare for register allocator.
+  UNUSED(instruction);
+  LOG(FATAL) << "Unreachable";
+}
+
+void InstructionCodeGeneratorX86::VisitBoundType(HBoundType* instruction) {
+  // Nothing to do, this should be removed during prepare for register allocator.
+  UNUSED(instruction);
+  LOG(FATAL) << "Unreachable";
+}
+
 }  // namespace x86
 }  // namespace art