Adding optimization to avoid image copy in SkSurface copy on write when content is discardable

tests/SurfaceTest.cpp

 
 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 #include "SkCanvas.h"
 #include "SkRRect.h"
 #include "SkSurface.h"
@@ skipping 130 matching lines @@
     // acquiring and releasing a snapshot without triggering a copy on write.
     SkSurface* surface = createSurface(surfaceType, context);
     SkAutoTUnref<SkSurface> aur_surface(surface);
     SkCanvas* canvas = surface->getCanvas();
     canvas->clear(1);
     surface->newImageSnapshot()->unref();  // Create and destroy SkImage
     canvas->clear(2);
 }
 static void TestSurfaceNoCanvas(skiatest::Reporter* reporter,
                                           SurfaceType surfaceType,
-                                          GrContext* context) {
+                                          GrContext* context,
+                                          SkSurface::ContentChangeMode mode) {
     // Verifies the robustness of SkSurface for handling use cases where calls
     // are made before a canvas is created.
     {
         // Test passes by not asserting
         SkSurface* surface = createSurface(surfaceType, context);
         SkAutoTUnref<SkSurface> aur_surface(surface);
-        surface->notifyContentChanged();
+        surface->notifyContentWillChange(mode);
         surface->validate();
     }
     {
         SkSurface* surface = createSurface(surfaceType, context);
         SkAutoTUnref<SkSurface> aur_surface(surface);
         SkImage* image1 = surface->newImageSnapshot();
         SkAutoTUnref<SkImage> aur_image1(image1);
         image1->validate();
         surface->validate();
-        surface->notifyContentChanged();
+        surface->notifyContentWillChange(mode);
         image1->validate();
         surface->validate();
         SkImage* image2 = surface->newImageSnapshot();
         SkAutoTUnref<SkImage> aur_image2(image2);
         image2->validate();
         surface->validate();
         REPORTER_ASSERT(reporter, image1 != image2);
     }
     
 }
 
 static void TestSurface(skiatest::Reporter* reporter, GrContextFactory* factory) {
     TestSurfaceCopyOnWrite(reporter, kRaster_SurfaceType, NULL);
     TestSurfaceCopyOnWrite(reporter, kPicture_SurfaceType, NULL);
     TestSurfaceWritableAfterSnapshotRelease(reporter, kRaster_SurfaceType, NULL);
     TestSurfaceWritableAfterSnapshotRelease(reporter, kPicture_SurfaceType, NULL);
-    TestSurfaceNoCanvas(reporter, kRaster_SurfaceType, NULL);
+    TestSurfaceNoCanvas(reporter, kRaster_SurfaceType, NULL, SkSurface::kDiscard_ContentChangeMode);
+    TestSurfaceNoCanvas(reporter, kRaster_SurfaceType, NULL, SkSurface::kRetain_ContentChangeMode);
 #if SK_SUPPORT_GPU
     if (NULL != factory) {
         GrContext* context = factory->get(GrContextFactory::kNative_GLContextType);
         TestSurfaceCopyOnWrite(reporter, kGpu_SurfaceType, context);
         TestSurfaceWritableAfterSnapshotRelease(reporter, kGpu_SurfaceType, context);
-        TestSurfaceNoCanvas(reporter, kGpu_SurfaceType, context);
+        TestSurfaceNoCanvas(reporter, kGpu_SurfaceType, context, SkSurface::kDiscard_ContentChangeMode);
+        TestSurfaceNoCanvas(reporter, kGpu_SurfaceType, context, SkSurface::kRetain_ContentChangeMode);
     }
 #endif
 }
 
 #include "TestClassDef.h"
 DEFINE_GPUTESTCLASS("Surface", SurfaceTestClass, TestSurface)