Rename NullHandle to ScopedNullHandle

This makes it clearer that is invalid to do things like:
Handle<T> h = ScopedNullHandle<T>();

Bug: 26233305
Change-Id: I6d8f54eae01ec2e901cb7043afa853ea77db79fe
diff --git a/compiler/optimizing/builder.h b/compiler/optimizing/builder.h
index ca71c32..73e85bb 100644
--- a/compiler/optimizing/builder.h
+++ b/compiler/optimizing/builder.h
@@ -80,7 +80,8 @@
         can_use_baseline_for_string_init_(true),
         compilation_stats_(nullptr),
         interpreter_metadata_(nullptr),
-        dex_cache_(NullHandle<mirror::DexCache>()) {}
+        null_dex_cache_(),
+        dex_cache_(null_dex_cache_) {}
 
   bool BuildGraph(const DexFile::CodeItem& code);
 
@@ -371,6 +372,7 @@
   const uint8_t* interpreter_metadata_;
 
   // Dex cache for dex_file_.
+  ScopedNullHandle<mirror::DexCache> null_dex_cache_;
   Handle<mirror::DexCache> dex_cache_;
 
   DISALLOW_COPY_AND_ASSIGN(HGraphBuilder);
diff --git a/compiler/optimizing/gvn_test.cc b/compiler/optimizing/gvn_test.cc
index de60cf2..78cb7d4 100644
--- a/compiler/optimizing/gvn_test.cc
+++ b/compiler/optimizing/gvn_test.cc
@@ -28,7 +28,7 @@
 TEST(GVNTest, LocalFieldElimination) {
   ArenaPool pool;
   ArenaAllocator allocator(&pool);
-  NullHandle<mirror::DexCache> dex_cache;
+  ScopedNullHandle<mirror::DexCache> dex_cache;
 
   HGraph* graph = CreateGraph(&allocator);
   HBasicBlock* entry = new (&allocator) HBasicBlock(graph);
@@ -113,7 +113,7 @@
 TEST(GVNTest, GlobalFieldElimination) {
   ArenaPool pool;
   ArenaAllocator allocator(&pool);
-  NullHandle<mirror::DexCache> dex_cache;
+  ScopedNullHandle<mirror::DexCache> dex_cache;
 
   HGraph* graph = CreateGraph(&allocator);
   HBasicBlock* entry = new (&allocator) HBasicBlock(graph);
@@ -196,7 +196,7 @@
 TEST(GVNTest, LoopFieldElimination) {
   ArenaPool pool;
   ArenaAllocator allocator(&pool);
-  NullHandle<mirror::DexCache> dex_cache;
+  ScopedNullHandle<mirror::DexCache> dex_cache;
 
   HGraph* graph = CreateGraph(&allocator);
   HBasicBlock* entry = new (&allocator) HBasicBlock(graph);
@@ -319,7 +319,7 @@
 TEST(GVNTest, LoopSideEffects) {
   ArenaPool pool;
   ArenaAllocator allocator(&pool);
-  NullHandle<mirror::DexCache> dex_cache;
+  ScopedNullHandle<mirror::DexCache> dex_cache;
 
   static const SideEffects kCanTriggerGC = SideEffects::CanTriggerGC();
 
diff --git a/compiler/optimizing/licm_test.cc b/compiler/optimizing/licm_test.cc
index 2bb769a..9ad003c 100644
--- a/compiler/optimizing/licm_test.cc
+++ b/compiler/optimizing/licm_test.cc
@@ -107,7 +107,7 @@
   BuildLoop();
 
   // Populate the loop with instructions: set/get field with different types.
-  NullHandle<mirror::DexCache> dex_cache;
+  ScopedNullHandle<mirror::DexCache> dex_cache;
   HInstruction* get_field = new (&allocator_) HInstanceFieldGet(parameter_,
                                                                 Primitive::kPrimLong,
                                                                 MemberOffset(10),
@@ -134,7 +134,7 @@
   BuildLoop();
 
   // Populate the loop with instructions: set/get field with same types.
-  NullHandle<mirror::DexCache> dex_cache;
+  ScopedNullHandle<mirror::DexCache> dex_cache;
   HInstruction* get_field = new (&allocator_) HInstanceFieldGet(parameter_,
                                                                 Primitive::kPrimLong,
                                                                 MemberOffset(10),
diff --git a/compiler/optimizing/register_allocator_test.cc b/compiler/optimizing/register_allocator_test.cc
index 080f970..8706854 100644
--- a/compiler/optimizing/register_allocator_test.cc
+++ b/compiler/optimizing/register_allocator_test.cc
@@ -472,7 +472,7 @@
                                   HInstruction** input2) {
   HGraph* graph = CreateGraph(allocator);
   HBasicBlock* entry = new (allocator) HBasicBlock(graph);
-  NullHandle<mirror::DexCache> dex_cache;
+  ScopedNullHandle<mirror::DexCache> dex_cache;
   graph->AddBlock(entry);
   graph->SetEntryBlock(entry);
   HInstruction* parameter = new (allocator) HParameterValue(
@@ -624,7 +624,7 @@
                                 HInstruction** field,
                                 HInstruction** ret) {
   HGraph* graph = CreateGraph(allocator);
-  NullHandle<mirror::DexCache> dex_cache;
+  ScopedNullHandle<mirror::DexCache> dex_cache;
   HBasicBlock* entry = new (allocator) HBasicBlock(graph);
   graph->AddBlock(entry);
   graph->SetEntryBlock(entry);