make allocPixels throw on failure

src/lazy/SkCachingPixelRef.cpp

Index: src/lazy/SkCachingPixelRef.cpp
diff --git a/src/lazy/SkCachingPixelRef.cpp b/src/lazy/SkCachingPixelRef.cpp
index 56431880c9f2dc2225f14176e035439d80e8f104..bd675324f155f5ed9981723465af91e14da3c3ba 100644
--- a/src/lazy/SkCachingPixelRef.cpp
+++ b/src/lazy/SkCachingPixelRef.cpp
@@ -46,7 +46,7 @@ bool SkCachingPixelRef::onNewLockPixels(LockRec* rec) {
     const SkImageInfo& info = this->info();
     if (!SkBitmapCache::Find(this->getGenerationID(), info.fWidth, info.fHeight, &fLockedBitmap)) {
         // Cache has been purged, must re-decode.
-        if (!fLockedBitmap.allocPixels(info, fRowBytes)) {
+        if (!fLockedBitmap.tryAllocPixels(info, fRowBytes)) {
             fErrorInDecoding = true;
             return false;
         }