Add capture snapshot as data to SkWriter32, use it to optimise record->playback.

tests/Writer32Test.cpp

 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkRandom.h"
 #include "SkReader32.h"
 #include "SkWriter32.h"
@@ skipping 262 matching lines @@
     writer.reset();
     testOverwriteT(reporter, &writer);
 }
 
 DEF_TEST(Writer32_misc, reporter) {
     test_reserve(reporter);
     test_string_null(reporter);
     test_ptr(reporter);
     test_rewind(reporter);
 }
+
+DEF_TEST(Writer32_snapshot, reporter) {
+    int32_t array[] = { 1, 2, 4, 11 };
+    SkSWriter32<sizeof(array) + 4> writer;
+    writer.write(array, sizeof(array));
+    check_contents(reporter, writer, array, sizeof(array));
+    const void* beforeData = writer.contiguousArray();
+    SkAutoDataUnref snapshot(writer.snapshotAsData());
+    // check the snapshot forced a copy of the static data
+    REPORTER_ASSERT(reporter, snapshot->data() != beforeData);
+    REPORTER_ASSERT(reporter, snapshot->size() == writer.bytesWritten());
+}
+
+DEF_TEST(Writer32_snapshot_dynamic, reporter) {
+    int32_t array[] = { 1, 2, 4, 11 };
+    SkWriter32 writer;
+    writer.write(array, sizeof(array));
+    check_contents(reporter, writer, array, sizeof(array));
+    // force a capacity increase so we can test COW behaviour
+    writer.write(array, sizeof(array));
+    writer.rewindToOffset(sizeof(array));
+    const void* beforeData = writer.contiguousArray();
+    SkAutoDataUnref snapshot(writer.snapshotAsData());
+    // check the snapshot still points to the same data as the writer
+    REPORTER_ASSERT(reporter, writer.contiguousArray() == beforeData);
+    REPORTER_ASSERT(reporter, snapshot->data() == beforeData);
+    REPORTER_ASSERT(reporter, snapshot->size() == writer.bytesWritten());
+    // write more data that would fit in the buffer
+    writer.write(array, sizeof(array));
+    // test it triggered COW anyway
+    REPORTER_ASSERT(reporter, writer.contiguousArray() != beforeData);
+}
+