cc: Fix flags access in ScopedRasterFlags.

If an image fails to decode on a shader, abort early instead of trying
to decode the flags further. Since Flags() returns nullptr based on
whether the decode failed, it was causing crashes.

R=enne@chromium.org

Bug: 824068,824058
Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;master.tryserver.blink:linux_trusty_blink_rel
Change-Id: I1040598df19c94a10a71a5b494f196abfffee2ab
Reviewed-on: https://chromium-review.googlesource.com/974480Reviewed-by: enne <enne@chromium.org>
Commit-Queue: Khushal <khushalsagar@chromium.org>
Cr-Commit-Position: refs/heads/master@{#544945}

cc/paint/scoped_raster_flags.cc

@@ -20,11 +20,15 @@ ScopedRasterFlags::ScopedRasterFlags(const PaintFlags* flags,
     // a mess. We decode image shaders at the correct scale but ignore that
     // during serialization and just use the original image.
     decode_stashing_image_provider_.emplace(image_provider);
+
+    // We skip the op if any images fail to decode.
     DecodeImageShader(ctm);
+    if (decode_failed_)
+      return;
     DecodeRecordShader(ctm, create_skia_shader);
+    if (decode_failed_)
+      return;
     DecodeFilter();
-
-    // We skip the op if any images fail to decode.
     if (decode_failed_)
       return;
   }

cc/paint/scoped_raster_flags.h

@@ -38,6 +38,7 @@ class CC_PAINT_EXPORT ScopedRasterFlags {
   void DecodeImageShader(const SkMatrix& ctm);
   void DecodeRecordShader(const SkMatrix& ctm, bool create_skia_shader);
   void DecodeFilter();
+
   void AdjustStrokeIfNeeded(const SkMatrix& ctm);
 
   PaintFlags* MutableFlags() {