Implement SkAshmemDiscardableMemory

gyp/tests.gyp

 # GYP file to build unit tests.
 {
   'includes': [
     'apptype_console.gypi',
   ],
   'targets': [
     {
       'target_name': 'tests',
       'type': 'executable',
       'include_dirs' : [
@@ skipping 38 matching lines @@
         '../tests/ClipStackTest.cpp',
         '../tests/ClipperTest.cpp',
         '../tests/ColorFilterTest.cpp',
         '../tests/ColorPrivTest.cpp',
         '../tests/ColorTest.cpp',
         '../tests/DataRefTest.cpp',
         '../tests/DeferredCanvasTest.cpp',
         '../tests/DequeTest.cpp',
         '../tests/DeviceLooperTest.cpp',
         '../tests/DiscardableMemoryPool.cpp',
+        '../tests/DiscardableMemoryTest.cpp',
         '../tests/DocumentTest.cpp',
         '../tests/DrawBitmapRectTest.cpp',
         '../tests/DrawPathTest.cpp',
         '../tests/DrawTextTest.cpp',
         '../tests/DynamicHashTest.cpp',
         '../tests/EmptyPathTest.cpp',
         '../tests/ErrorTest.cpp',
         '../tests/FillPathTest.cpp',
         '../tests/FitsInTest.cpp',
         '../tests/FlatDataTest.cpp',
@@ skipping 106 matching lines @@
       'conditions': [
         [ 'skia_gpu == 1', {
           'include_dirs': [
             '../src/gpu',
           ],
         }],
       ],
     },
   ],
 }