update_engine: Refactor inplace payload generator algorithm code.

Create a class, InplaceGenerator, that contains all functionality
related to the inplace delta generation method (minor version 1).

BUG=chromium:459701
TEST=`FEATURES=test emerge-link update_engine`

Change-Id: Ib742f70030d6c2fcb1cc3138e0f4aef54eca6975
Reviewed-on: https://chromium-review.googlesource.com/251621
Reviewed-by: Alex Deymo <deymo@chromium.org>
Commit-Queue: Allie Wood <alliewood@chromium.org>
Tested-by: Allie Wood <alliewood@chromium.org>
diff --git a/update_engine.gyp b/update_engine.gyp
index 4212c5b..6fe642f 100644
--- a/update_engine.gyp
+++ b/update_engine.gyp
@@ -281,6 +281,7 @@
         'payload_generator/filesystem_iterator.cc',
         'payload_generator/full_update_generator.cc',
         'payload_generator/graph_utils.cc',
+        'payload_generator/inplace_generator.cc',
         'payload_generator/metadata.cc',
         'payload_generator/payload_signer.cc',
         'payload_generator/tarjan.cc',
@@ -373,6 +374,7 @@
             'payload_generator/filesystem_iterator_unittest.cc',
             'payload_generator/full_update_generator_unittest.cc',
             'payload_generator/graph_utils_unittest.cc',
+            'payload_generator/inplace_generator_unittest.cc',
             'payload_generator/metadata_unittest.cc',
             'payload_generator/payload_signer_unittest.cc',
             'payload_generator/tarjan_unittest.cc',