Resolve inconsistent treatment of stubs in kAppJIT snapshots in favor of write stubs in the snapsho…

runtime/vm/snapshot.cc

Index: runtime/vm/snapshot.cc
diff --git a/runtime/vm/snapshot.cc b/runtime/vm/snapshot.cc
index d720d0ef67efd9d017814adfff8599e7f16c44bf..3d8f5757eabdcf613098d17d55dbf42ed9a5d400 100644
--- a/runtime/vm/snapshot.cc
+++ b/runtime/vm/snapshot.cc
@@ -685,28 +685,17 @@ RawObject* SnapshotReader::NewInteger(int64_t value) {
 }
 
 
-int32_t ImageWriter::GetOffsetFor(RawInstructions* instructions,
-                                  RawCode* code) {
-#if defined(PRODUCT)
-  // Instructions are only dedup in product mode because it obfuscates profiler

[rmacnak, 2017/05/03 19:53:53]

This comment is misleading. To effectively deduplicate instructions, we need to
both

1) Update Code objects to point to canonical Instruction objects
2) Use the same text offset if we encounter the same Instruction object multiple
times

1 is achieved by ProgramVisitor::DedupInstructions() and that only runs in
PRODUCT mode.
2 was achieved by this code but is now achieved by the use of the object id
table.

-  // results.
-  for (intptr_t i = 0; i < instructions_.length(); i++) {
-    if (instructions_[i].raw_insns_ == instructions) {
-      return instructions_[i].offset_;
-    }
-  }
-#endif
-
+int32_t ImageWriter::GetTextOffsetFor(RawInstructions* instructions,
+                                      RawCode* code) {
   intptr_t heap_size = instructions->Size();
   intptr_t offset = next_offset_;
   next_offset_ += heap_size;
   instructions_.Add(InstructionsData(instructions, code, offset));
-
   return offset;
 }
 
 
-int32_t ImageWriter::GetObjectOffsetFor(RawObject* raw_object) {
+int32_t ImageWriter::GetDataOffsetFor(RawObject* raw_object) {
   intptr_t heap_size = raw_object->Size();
   intptr_t offset = next_object_offset_;
   next_object_offset_ += heap_size;