Fix last_range != range_for_next_append_ DCHECK in SourceBufferStream.

Added a condition to avoid the DCHECK for a valid situation where the
check should have been applied.. A test was added to capture the
specific case that was triggering the DCHECK.

BUG=303413
TEST=SourceBufferStreamTest.Remove_PreviousAppendDestroyedAndOverwriteExistingRange

Review URL: https://codereview.chromium.org/58663003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@232998 0039d316-1c4b-4281-b951-d872f2087c98

media/filters/source_buffer_stream.cc

@@ -391,7 +391,7 @@ void SourceBufferStream::OnNewMediaSegment(
                              media_segment_start_time)) {
     last_appended_buffer_timestamp_ = kNoTimestamp();
     last_appended_buffer_is_keyframe_ = false;
-  } else {
+  } else if (last_range != ranges_.end()) {
     DCHECK(last_range == range_for_next_append_);
   }
 }

media/filters/source_buffer_stream_unittest.cc

@@ -3225,6 +3225,31 @@ TEST_F(SourceBufferStreamTest, Remove_GOPBeingAppended) {
   CheckExpectedBuffers("240K 270 300");
 }
 
+
+TEST_F(SourceBufferStreamTest,
+       Remove_PreviousAppendDestroyedAndOverwriteExistingRange) {
+  SeekToTimestamp(base::TimeDelta::FromMilliseconds(90));
+
+  NewSegmentAppend("90K 120 150");
+  CheckExpectedRangesByTimestamp("{ [90,180) }");
+
+  // Append a segment before the previously appended data.
+  NewSegmentAppend("0K 30 60");
+
+  // Verify that the ranges get merged.
+  CheckExpectedRangesByTimestamp("{ [0,180) }");
+
+  // Remove the data from the last append.
+  RemoveInMs(0, 90, 360);
+  CheckExpectedRangesByTimestamp("{ [90,180) }");
+
+  // Append a new segment that follows the removed segment and
+  // starts at the beginning of the range left over from the
+  // remove.
+  NewSegmentAppend("90K 121 151");
+  CheckExpectedBuffers("90K 121 151");
+}
+
 // TODO(vrk): Add unit tests where keyframes are unaligned between streams.
 // (crbug.com/133557)