Revert "update_engine: Merge contiguous operations."

This reverts commit 6a3ea94766bb4972abbd629779914d80dada1245.

The CL is suspected to close the tree due to paygen failures.
See comments inline (delta_diff_generator.cc) for the culprit.

BUG=chromium:486497
TEST=trybot

Change-Id: Iaed694a79371e7de208b0de90f8e9cefd61dd7e6
Reviewed-on: https://chromium-review.googlesource.com/270183
Trybot-Ready: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Cheng-Yi Chiang <cychiang@chromium.org>
Commit-Queue: Cheng-Yi Chiang <cychiang@chromium.org>
Tested-by: Cheng-Yi Chiang <cychiang@chromium.org>
diff --git a/delta_performer_unittest.cc b/delta_performer_unittest.cc
index 381f777..a72061b 100644
--- a/delta_performer_unittest.cc
+++ b/delta_performer_unittest.cc
@@ -111,6 +111,9 @@
   kValidOperationData,
 };
 
+// Chuck size used for full payloads during test.
+size_t kDefaultFullChunkSize = 1024 * 1024;
+
 }  // namespace
 
 class DeltaPerformerTest : public ::testing::Test {
@@ -540,7 +543,7 @@
 
     } else {
       if (payload_config.chunk_size == -1)
-        payload_config.chunk_size = kDefaultChunkSize;
+        payload_config.chunk_size = kDefaultFullChunkSize;
     }
     payload_config.target.rootfs_part = state->b_img;
     payload_config.target.rootfs_mountpt = b_mnt;