cc: fix paint op perf tests

After the client/service paint cache entries were added, these tests
started failing.  Fix this by clearing the client paint cache on every
iteration so that each op has to always serialize cached subtypes.

Change-Id: I7dfae5b5ae34864f77ae1fb28793b1ab2db94c86
Reviewed-on: https://chromium-review.googlesource.com/c/1343502Reviewed-by: Khushal <khushalsagar@chromium.org>
Commit-Queue: enne <enne@chromium.org>
Cr-Commit-Position: refs/heads/master@{#609550}

cc/paint/paint_op_perftest.cc

@@ -60,6 +60,9 @@ class PaintOpPerfTest : public testing::Test {
           test_options_provider.max_texture_bytes());
       serializer.Serialize(&buffer, nullptr, preamble);
       bytes_written = serializer.written();
+
+      // Force client paint cache entries to be written every time.
+      test_options_provider.client_paint_cache()->PurgeAll();
       timer_.NextLap();
     } while (!timer_.HasTimeLimitExpired());
     CHECK_GT(bytes_written, 0u);
@@ -81,6 +84,7 @@ class PaintOpPerfTest : public testing::Test {
             to_read, remaining_read_bytes, deserialized_data_.get(),
             sizeof(LargestPaintOp), &bytes_read,
             test_options_provider.deserialize_options());
+        CHECK(deserialized_op);
         deserialized_op->DestroyThis();
 
         DCHECK_GE(remaining_read_bytes, bytes_read);