Fix PartialCircularBuffer OOB memcpy().

chrome/common/partial_circular_buffer_unittest.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // The test buffer data is 52 bytes, wrap position is set to 20 (this is
 // arbitrarily chosen). The total buffer size is allocated dynamically based on
 // the actual header size. This gives:
 // Header of some size, non-wrapping part 20 bytes, wrapping part 32 bytes.
 // As input data, a 14 byte array is used and repeatedly written. It's chosen
 // not to be an integer factor smaller than the wrapping part. This ensures that
@@ skipping 171 matching lines @@
   InitReadBuffer();
 
   uint8 output_data[sizeof(kInputData)] = {0};
   EXPECT_EQ(sizeof(output_data),
             pcb_read_->Read(output_data, sizeof(output_data)));
 
   EXPECT_EQ(0, memcmp(kInputData, output_data, sizeof(kInputData)));
 
   EXPECT_EQ(0u, pcb_read_->Read(output_data, sizeof(output_data)));
 }
+
+TEST_F(PartialCircularBufferTest, WrapTwiceWithSingleWrite) {
+  const size_t kInputSize = sizeof(kInputData);
+  const size_t kLargeSize = kInputSize * 7;
+  uint8 large_input[kLargeSize] = {0};
+  for (size_t offset = 0; offset < kLargeSize; offset += kInputSize)
+    memcpy(large_input + offset, kInputData, kInputSize);
+
+  InitWriteBuffer(false);
+  pcb_write_->Write(large_input, kLargeSize);
+  InitReadBuffer();
+
+  uint8 output_data[sizeof(kOutputRefDataWrap)] = {0};
+  EXPECT_EQ(sizeof(output_data),
+            pcb_read_->Read(output_data, sizeof(output_data)));
+
+  EXPECT_EQ(0, memcmp(kOutputRefDataWrap, output_data, sizeof(output_data)));
+
+  EXPECT_EQ(0u, pcb_read_->Read(output_data, sizeof(output_data)));
+}
+