content: Fix problem with implementation of MergeIntoFreeList.

content/common/discardable_shared_memory_heap.cc

Index: content/common/discardable_shared_memory_heap.cc
diff --git a/content/common/discardable_shared_memory_heap.cc b/content/common/discardable_shared_memory_heap.cc
index fc97c2bd186e16d219a48b6693e0bbc6b5d3ba73..c854a96b042d86192c93d5aa9a6ce053005771ce 100644
--- a/content/common/discardable_shared_memory_heap.cc
+++ b/content/common/discardable_shared_memory_heap.cc
@@ -75,7 +75,8 @@ void DiscardableSharedMemoryHeap::MergeIntoFreeList(scoped_ptr<Span> span) {
     scoped_ptr<Span> prev = RemoveFromFreeList(prev_it->second);
     DCHECK_EQ(prev->start_ + prev->length_, span->start_);
     UnregisterSpan(prev.get());
-    spans_.erase(span->start_);
+    if (span->length_ > 1)
+      spans_.erase(span->start_);
     span->start_ -= prev->length_;
     span->length_ += prev->length_;
     spans_[span->start_] = span.get();