Alter layer hoisting to only hoist layers for one canvas at a time

tests/GpuLayerCacheTest.cpp

 /*
 * Copyright 2014 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */
 
 #if SK_SUPPORT_GPU
 
 #include "GrContext.h"
@@ skipping 48 matching lines @@
 
 static void lock_layer(skiatest::Reporter* reporter,
                        GrLayerCache* cache,
                        GrCachedLayer* layer) {
     // Make the layer 512x512 (so it can be atlased)
     GrTextureDesc desc;
     desc.fWidth = 512;
     desc.fHeight = 512;
     desc.fConfig = kSkia8888_GrPixelConfig;
 
-    bool needsRerendering = cache->lock(layer, desc, false);
+    bool needsRerendering;
+    bool inAtlas = cache->tryToAtlas(layer, desc, &needsRerendering);
+    if (!inAtlas) {
+        cache->lock(layer, desc, &needsRerendering);
+    }
     REPORTER_ASSERT(reporter, needsRerendering);
 
-    needsRerendering = cache->lock(layer, desc, false);
+    cache->lock(layer, desc, &needsRerendering);
     REPORTER_ASSERT(reporter, !needsRerendering);
 
     REPORTER_ASSERT(reporter, layer->texture());
     REPORTER_ASSERT(reporter, layer->locked());
 
     cache->addUse(layer);
 
     REPORTER_ASSERT(reporter, 1 == TestingAccess::Uses(layer));
 }
 
@@ skipping 130 matching lines @@
 
         picture.reset(NULL);
         cache.processDeletedPictures();
 
         REPORTER_ASSERT(reporter, TestingAccess::NumLayers(&cache) == 0);
         // TODO: add VRAM/resource cache check here
     }
 }
 
 #endif