Make SkImageGenerator::getPixels() return an enum.

src/lazy/SkDiscardablePixelRef.cpp

Index: src/lazy/SkDiscardablePixelRef.cpp
diff --git a/src/lazy/SkDiscardablePixelRef.cpp b/src/lazy/SkDiscardablePixelRef.cpp
index b51daa6faa7ded8aa34649ef7e381662a2c76d81..50988587a7c1030cf3fd56727e104011f31b4870 100644
--- a/src/lazy/SkDiscardablePixelRef.cpp
+++ b/src/lazy/SkDiscardablePixelRef.cpp
@@ -64,11 +64,17 @@ bool SkDiscardablePixelRef::onNewLockPixels(LockRec* rec) {
     SkPMColor colors[256];
     int colorCount = 0;
 
-    if (!fGenerator->getPixels(info, pixels, fRowBytes, colors, &colorCount)) {
-        fDiscardableMemory->unlock();
-        SkDELETE(fDiscardableMemory);
-        fDiscardableMemory = NULL;
-        return false;
+    const SkImageGenerator::Result result = fGenerator->getPixels(info, pixels, fRowBytes,
+                                                                  colors, &colorCount);
+    switch (result) {
+        case SkImageGenerator::kSuccess:
+        case SkImageGenerator::kIncompleteInput:
+            break;
+        default:
+            fDiscardableMemory->unlock();
+            SkDELETE(fDiscardableMemory);
+            fDiscardableMemory = NULL;
+            return false;
     }
 
     // Note: our ctable is not purgeable, as it is not stored in the discardablememory block.