update_engine: Merge contiguous operations.

Merges operations of type SOURCE_COPY, REPLACE, or REPLACE_BZ if they
have the same type, are contiguous, have only one destination extent,
and their combined block count does not exceed the chunk size.

BUG=chromium:461651
TEST=`cros flash --src-image-to-delta`, checking generated payloads
using `cros payload show --list_ops`, unit tests.
CQ-DEPEND=CL:269134

Change-Id: I5f71e6828561f2e0a6a8ab3e3aae4c362ea2ddde
Reviewed-on: https://chromium-review.googlesource.com/269604
Reviewed-by: Alex Deymo <deymo@chromium.org>
Commit-Queue: Allie Wood <alliewood@chromium.org>
Trybot-Ready: Allie Wood <alliewood@chromium.org>
Tested-by: Allie Wood <alliewood@chromium.org>
diff --git a/delta_performer_unittest.cc b/delta_performer_unittest.cc
index 87d98de..4739cb2 100644
--- a/delta_performer_unittest.cc
+++ b/delta_performer_unittest.cc
@@ -111,9 +111,6 @@
   kValidOperationData,
 };
 
-// Chuck size used for full payloads during test.
-size_t kDefaultFullChunkSize = 1024 * 1024;
-
 }  // namespace
 
 class DeltaPerformerTest : public ::testing::Test {
@@ -546,7 +543,7 @@
 
     } else {
       if (payload_config.chunk_size == -1)
-        payload_config.chunk_size = kDefaultFullChunkSize;
+        payload_config.chunk_size = kDefaultChunkSize;
     }
     payload_config.target.rootfs_part = state->b_img;
     payload_config.target.rootfs_mountpt = b_mnt;