[Isolates] Merge from bleeding_edge to isolates, revisions 6100-6300.

src/data-flow.h

Index: src/data-flow.h
===================================================================
--- src/data-flow.h	(revision 6941)
+++ src/data-flow.h	(working copy)
@@ -112,10 +112,13 @@
   }
 
   void CopyFrom(const BitVector& other) {
-    ASSERT(other.length() == length());
-    for (int i = 0; i < data_length_; i++) {
+    ASSERT(other.length() <= length());
+    for (int i = 0; i < other.data_length_; i++) {
       data_[i] = other.data_[i];
     }
+    for (int i = other.data_length_; i < data_length_; i++) {
+      data_[i] = 0;
+    }
   }
 
   bool Contains(int i) const {