Fix crash in tests on valgrind bot

I believe this will fix the following crash on the valgrind bot:

Failed to open X display.
Invalid read of size 8
at 0x5813E3: SkSurface::getCanvas() (SkSurface_Base.h:75)
by 0x495D8B: skiatest::SurfaceTestClass::onRun(skiatest::Reporter*) (SurfaceTest.cpp:159)
by 0x4966F2: skiatest::Test::run() (Test.cpp:109)
by 0x48FD90: SkTestRunnable::run() (skia_test.cpp:155)
by 0x48F736: tool_main(int, char**) (skia_test.cpp:246)
by 0x48F912: main (skia_test.cpp:276)
Address 0x18 is not stack'd, malloc'd or (recently) free'd

Process terminating with default action of signal 11 (SIGSEGV)
Access not within mapped region at address 0x18
at 0x5813E3: SkSurface::getCanvas() (SkSurface_Base.h:75)
by 0x495D8B: skiatest::SurfaceTestClass::onRun(skiatest::Reporter*) (SurfaceTest.cpp:159)
by 0x4966F2: skiatest::Test::run() (Test.cpp:109)
by 0x48FD90: SkTestRunnable::run() (skia_test.cpp:155)
by 0x48F736: tool_main(int, char**) (skia_test.cpp:246)
by 0x48F912: main (skia_test.cpp:276)

[jvanverth1, 2013-11-12 13:42:23]

lgtm

[robertphillips, 2013-11-12 13:51:18]

committed as r12234