Fix leak in BlurTest

Before:

40,000 bytes in 4 blocks are definitely lost in loss record 47 of 48
   at 0x4C2B6CD: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
   by 0x79D98A: sk_malloc_flags(unsigned long, unsigned int) (SkMemory_malloc.cpp:45)
   by 0x79D915: sk_malloc_throw(unsigned long) (SkMemory_malloc.cpp:31)
   by 0x5C001B: SkMask::AllocImage(unsigned long) (SkMask.cpp:40)
   by 0x41922C: ground_truth_2d(int, int, float, int*, int) (BlurTest.cpp:167)
   by 0x419C6D: test_sigma_range(skiatest::Reporter*, GrContextFactory*) (BlurTest.cpp:357)
   by 0x419F6E: test_blur(skiatest::Reporter*, GrContextFactory*) (BlurTest.cpp:384)
   by 0x41A81A: skiatest::BlurTestClass::onRun(skiatest::Reporter*) (BlurTest.cpp:388)
   by 0x4C9539: skiatest::Test::run() (Test.cpp:109)
   by 0x4BEEC5: SkTestRunnable::run() (skia_test.cpp:155)
   by 0x4BE3EB: tool_main(int, char**) (skia_test.cpp:246)
   by 0x4BE5DC: main (skia_test.cpp:276)

56,836 bytes in 4 blocks are definitely lost in loss record 48 of 48
   at 0x4C2B6CD: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
   by 0x79D98A: sk_malloc_flags(unsigned long, unsigned int) (SkMemory_malloc.cpp:45)
   by 0x79D915: sk_malloc_throw(unsigned long) (SkMemory_malloc.cpp:31)
   by 0x5C001B: SkMask::AllocImage(unsigned long) (SkMask.cpp:40)
   by 0x693B9B: SkBlurMask::BlurGroundTruth(float, SkMask*, SkMask const&, SkBlurMask::Style, SkIPoint*) (SkBlurMask.cpp:920)
   by 0x419277: ground_truth_2d(int, int, float, int*, int) (BlurTest.cpp:172)
   by 0x419C6D: test_sigma_range(skiatest::Reporter*,    by 0x419F6E: test_blur(skiatest::Reporter*, GrContextFactory*) (BlurTest.cpp:384)
   by 0x41A81A: skiatest::BlurTestClass::onRun(skiatest::Reporter*) (BlurTest.cpp:388)
   by 0x4C9539: skiatest::Test::run() (Test.cpp:109)
   by 0x4BEEC5: SkTestRunnable::run() (skia_test.cpp:155)
   by 0x4BE3EB: tool_main(int, char**) (skia_test.cpp:246)

[robertphillips, 2013-10-11 14:11:41]

added Brian

[humper, 2013-10-11 14:35:55]

On 2013/10/11 14:11:41, robertphillips wrote:
> added Brian

lgtm

[robertphillips, 2013-10-11 14:39:01]

committed as r11725