Make peeking before the head of OffsetByteQueue a hard error.

BUG=
TEST=OffsetByteQueueTest


Review URL: https://chromiumcodereview.appspot.com/10823069

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@149293 0039d316-1c4b-4281-b951-d872f2087c98

media/mp4/offset_byte_queue.cc

@@ -37,6 +37,7 @@ void OffsetByteQueue::Pop(int count) {
 }
 
 void OffsetByteQueue::PeekAt(int64 offset, const uint8** buf, int* size) {
+  DCHECK(offset >= head());
   if (offset < head() || offset >= tail()) {
     *buf = NULL;
     *size = 0;

media/mp4/offset_byte_queue_unittest.cc

@@ -48,10 +48,6 @@ TEST_F(OffsetByteQueueTest, TestPeekAt) {
   const uint8* buf;
   int size;
 
-  queue_->PeekAt(128, &buf, &size);
-  EXPECT_EQ(NULL, buf);
-  EXPECT_EQ(0, size);
-
   queue_->PeekAt(400, &buf, &size);
   EXPECT_EQ(queue_->tail() - 400, size);
   EXPECT_EQ(400 - 256, buf[0]);