SkDiscardableMemoryPool to abstract class

Motivation - we want to keep our public headers small.

R=scroggo@google.com, reed@google.com

Author: halcanary@google.com

Review URL: https://codereview.chromium.org/223403012

git-svn-id: http://skia.googlecode.com/svn/trunk@14063 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/tests/ImageCacheTest.cpp b/tests/ImageCacheTest.cpp
index 43a5e70..92d0b51 100644
--- a/tests/ImageCacheTest.cpp
+++ b/tests/ImageCacheTest.cpp
@@ -81,6 +81,7 @@
 
 static SkDiscardableMemoryPool* gPool;
 static SkDiscardableMemory* pool_factory(size_t bytes) {
+    SkASSERT(gPool);
     return gPool->create(bytes);
 }
 
@@ -92,8 +93,9 @@
         test_cache(reporter, cache, true);
     }
     {
-        SkDiscardableMemoryPool pool(defLimit);
-        gPool = &pool;
+        SkAutoTUnref<SkDiscardableMemoryPool> pool(
+                SkDiscardableMemoryPool::Create(defLimit, NULL));
+        gPool = pool.get();
         SkScaledImageCache cache(pool_factory);
         test_cache(reporter, cache, true);
     }