- Use size_t for frame_size() (fixes warnings elsewhere)
- Remove unnecessary use of const.

Change-Id: Id2cba182ac3fd2f67d25fd1db3a0bc3e1eda040b

Suggested by James Zern to clear out cpplint warnings for all unit
test code.

Change-Id: I731a3fa4d2a257eb9ef733426ba84286fbd7ea34

Change-Id: If908328c1dbbb5bd84c57e30fab1cda1804933e4

if the caller did not abort after an ASSERT failure in Begin()
FillFrame() would segfault.

Change-Id: I2d3f5a0918611bbd081be6f686dea19c56695073

Got 61 test vectors from vp8-test-vectors.git
(http://git.chromium.org/gitweb/?p=webm/vp8-test-vectors.git)

Added decoder test vectors downloading in unit tests. Uploaded
the test vectors and their md5 files to WebM website.
  $ gsutil cp *.* gs://downloads.webmproject.org/test_data/libvpx

Added their sha1sum to the test/test-data.sha1 file.

In unit tests, download the test vectors to LIBVPX_TEST_DATA_PATH.

Test_vector_test goes through the test vectors, decodes them, and
compute the md5 checksums. The checksums are compared with the
expected md5 checksums to tell if the decoder decodes correctly.

Change-Id: Ia1e84f9347ddf1d4a02e056c0fee7d28dccfae15