[IndexedDB] Fix cursor pooling IsValid().

We accidentally didn't handle the case where the iterator was evicted
and invalid. This is now much more explicit and tested.

R=pwnall,cmumford
BUG=705837

Review-Url: https://codereview.chromium.org/2786463002
Cr-Commit-Position: refs/heads/master@{#460526}

content/browser/indexed_db/leveldb/leveldb_iterator_impl.cc

@@ -38,8 +38,16 @@ leveldb::Status LevelDBIteratorImpl::CheckStatus() {
 }
 
 bool LevelDBIteratorImpl::IsValid() const {
-  return iterator_state_ == IteratorState::EVICTED_AND_VALID ||
-         iterator_->Valid();
+  switch (iterator_state_) {
+    case IteratorState::EVICTED_AND_VALID:
+      return true;
+    case IteratorState::EVICTED_AND_INVALID:
+      return false;
+    case IteratorState::ACTIVE:
+      return iterator_->Valid();
+  }
+  NOTREACHED();
+  return false;
 }
 
 leveldb::Status LevelDBIteratorImpl::SeekToLast() {

content/browser/indexed_db/leveldb/leveldb_transaction_unittest.cc

@@ -250,8 +250,6 @@ TEST_F(LevelDBTransactionTest, IterationWithEvictedCursors) {
   EXPECT_FALSE(evicted_normal_location->IsDetached());
   EXPECT_FALSE(evicted_before_start->IsDetached());
   EXPECT_FALSE(evicted_after_end->IsDetached());
-  EXPECT_FALSE(evicted_before_start->IsValid());
-  EXPECT_FALSE(evicted_after_end->IsValid());
 
   // Should purge all of our earlier iterators.
   it1->Seek("key1");
@@ -262,6 +260,10 @@ TEST_F(LevelDBTransactionTest, IterationWithEvictedCursors) {
   EXPECT_TRUE(evicted_before_start->IsDetached());
   EXPECT_TRUE(evicted_after_end->IsDetached());
 
+  EXPECT_FALSE(evicted_before_start->IsValid());
+  EXPECT_TRUE(evicted_normal_location->IsValid());
+  EXPECT_FALSE(evicted_after_end->IsValid());
+
   // Check we don't need to reload for just the key.
   EXPECT_EQ("key1", evicted_normal_location->Key());
   EXPECT_TRUE(evicted_normal_location->IsDetached());