Compile-time tuning

Specialized the dataflow iterators and did a few other minor tweaks.
Showing ~5% compile-time improvement in a single-threaded environment;
less in multi-threaded (presumably because we're blocked by something
else).

Change-Id: I2e2ed58d881414b9fc97e04cd0623e188259afd2
diff --git a/compiler/dex/growable_array.h b/compiler/dex/growable_array.h
index 8e2abfb..9053285 100644
--- a/compiler/dex/growable_array.h
+++ b/compiler/dex/growable_array.h
@@ -150,6 +150,11 @@
 
     size_t Size() const { return num_used_; }
 
+    void SetSize(size_t new_size) {
+      Resize(new_size);
+      num_used_ = new_size;
+    }
+
     T* GetRawStorage() const { return elem_list_; }
 
     static void* operator new(size_t size, ArenaAllocator* arena) {