Split payload application code into a subdirectory.

This patch splits from the main libupdate_engine code the part that
is strictly used to download and apply a payload into a new static
library, moving the code to subdirectories. The new library is divided
in two subdirectories: common/ and payload_consumer/, and should not
depend on other update_engine files outside those two subdirectories.
The main difference between those two is that the common/ tools are more
generic and not tied to the payload consumer process, but otherwise they
are both compiled together.

There are still dependencies from the new libpayload_consumer library
into the main directory files and DBus generated files. Those will be
addressed in follow up CLs.

Bug: 25197634
Test: FEATURES=test emerge-link update_engine; `mm` on Brillo.

Change-Id: Id8d0204ea573627e6e26ca9ea17b9592ca95bc23
diff --git a/payload_generator/block_mapping.cc b/payload_generator/block_mapping.cc
index 81ad4bb..ff10f0b 100644
--- a/payload_generator/block_mapping.cc
+++ b/payload_generator/block_mapping.cc
@@ -24,7 +24,7 @@
 #include <string>
 #include <vector>
 
-#include "update_engine/utils.h"
+#include "update_engine/common/utils.h"
 
 using std::string;
 using std::vector;
@@ -57,7 +57,7 @@
 bool BlockMapping::AddManyDiskBlocks(int fd,
                                      off_t initial_byte_offset,
                                      size_t num_blocks,
-                                     std::vector<BlockId>* block_ids) {
+                                     vector<BlockId>* block_ids) {
   bool ret = true;
   block_ids->resize(num_blocks);
   for (size_t block = 0; block < num_blocks; block++) {