use SkStream factory for files, and check for null (file-not-found) speedup sampleapp's animation

BUG=

Review URL: https://codereview.chromium.org/16173003

git-svn-id: http://skia.googlecode.com/svn/trunk@9327 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/samplecode/SampleApp.cpp b/samplecode/SampleApp.cpp
index 40c9d1f..c5910ef 100644
--- a/samplecode/SampleApp.cpp
+++ b/samplecode/SampleApp.cpp
@@ -74,7 +74,7 @@
 #endif
 
 #define ANIMATING_EVENTTYPE "nextSample"
-#define ANIMATING_DELAY     750
+#define ANIMATING_DELAY     250
 
 #ifdef SK_DEBUG
     #define FPS_REPEAT_MULTIPLIER   1