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/payload_generator/metadata.cc b/payload_generator/metadata.cc
index 7a6493c..a96071a 100644
--- a/payload_generator/metadata.cc
+++ b/payload_generator/metadata.cc
@@ -19,6 +19,7 @@
 #include "update_engine/payload_generator/delta_diff_generator.h"
 #include "update_engine/payload_generator/ext2_utils.h"
 #include "update_engine/payload_generator/graph_utils.h"
+#include "update_engine/payload_generator/inplace_generator.h"
 #include "update_engine/utils.h"
 
 using base::StringPrintf;
@@ -192,7 +193,7 @@
   CHECK((*graph)[vertex].op.has_type());
   (*graph)[vertex].file_name = metadata_name;
 
-  TEST_AND_RETURN_FALSE(DeltaDiffGenerator::AddInstallOpToBlocksVector(
+  TEST_AND_RETURN_FALSE(InplaceGenerator::AddInstallOpToBlocksVector(
       (*graph)[vertex].op,
       *graph,
       vertex,