make allocPixels throw on failure

BUG=skia:
R=mtklein@google.com, fmalita@google.com, fmalita@chromium.org

Author: reed@google.com

Review URL: https://codereview.chromium.org/510423005
diff --git a/src/lazy/SkCachingPixelRef.cpp b/src/lazy/SkCachingPixelRef.cpp
index 5643188..bd67532 100644
--- a/src/lazy/SkCachingPixelRef.cpp
+++ b/src/lazy/SkCachingPixelRef.cpp
@@ -46,7 +46,7 @@
     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;
         }