A simpler scheme for garbage collection of ureachable phi inputs.

runtime/vm/growable_array.h

Index: runtime/vm/growable_array.h
diff --git a/runtime/vm/growable_array.h b/runtime/vm/growable_array.h
index 7a2b7b266226f3742d820e78f63a69c1d238335b..2f196f7fe875ceb7a58b171d8842071cd2780d46 100644
--- a/runtime/vm/growable_array.h
+++ b/runtime/vm/growable_array.h
@@ -73,10 +73,10 @@ class BaseGrowableArray : public B {
     length_ = 0;
   }
 
-  void RemoveFirst() {
-    ASSERT(length_ > 0);
+  void Remove(intptr_t idx) {
+    ASSERT(length_ > idx);
     length_--;
-    for (int i = 0; i < length_; i++) {
+    for (int i = idx; i < length_; i++) {
       data_[i] = data_[i + 1];
     }
   }