Avoid a loop in writeString and writePad by zeroing padding first.

Avoid a loop in writeString and writePad by zeroing padding first.

Also add a benchmark to time the new improved writeString. Before
my change the bench took ~1.23ms and afterwards it takes ~.95ms.

Add some testing to ensure that writePad works properly.

TEST=Writer32Test, WriterBench

Committed: https://code.google.com/p/skia/source/detail?r=4742

[reed1, 2012-07-24 19:22:58]

nice change/addition overall. minor nit on strlen caching. other than that, lgtm

https://codereview.appspot.com/6438045/diff/1/bench/WriterBench.cpp
File bench/WriterBench.cpp (right):

https://codereview.appspot.com/6438045/diff/1/bench/WriterBench.cpp#newcode25
bench/WriterBench.cpp:25: for (int i = 0; i < SkBENCHLOOP(800); i++) {
cache len outside of the loop?

[Leon, 2012-07-24 20:43:42]

https://codereview.appspot.com/6438045/diff/1/bench/WriterBench.cpp
File bench/WriterBench.cpp (right):

https://codereview.appspot.com/6438045/diff/1/bench/WriterBench.cpp#newcode25
bench/WriterBench.cpp:25: for (int i = 0; i < SkBENCHLOOP(800); i++) {
On 2012/07/24 19:22:59, reed1 wrote:
> cache len outside of the loop?

Done.