update_engine resize dynamic partitions during OTA.

update_engine uses device mapper to resize dynamic partitions
before opening the devices to apply the update.

* DeltaPerformer calls BootControlInterface::InitPartitionMetadata
  when parsing the update manifest. The implementation for
  BootControlAndroid::InitPartitionMetadata does the following
  if sizes for dynamic partitions are incorrect (assuming updating
  from slot A to B):
  * Load metadata from metadata slot A
  * Delete all extents of partitions at slot B (with _b suffix)
  * Add extents for partitions at slot B
  * Write metadata to metadata slot B
  * Re-map all partitions at slot B using metadata slot B with
    force_writable = true
* BootControlAndroid::GetPartitionDevice() checks device-mapper
  before returning static partitions.
* PostinstallRunnerAction::Cleanup calls BootControlInterface::Cleanup
  which unmaps all partitions at slot B.

A partition "foo" is considered dynamic if foo_a exists as a dynamic
partition OR foo_b does NOT exist as a static partition.

Bug: 110717529

Test: manual ota
Test: update_engine_unittests --gtest_filter=*BootControlAndroid*
Change-Id: I50f410b486a874242663624801c3694151bdda18
diff --git a/common/boot_control_stub.cc b/common/boot_control_stub.cc
index 2de0c82..2e326e5 100644
--- a/common/boot_control_stub.cc
+++ b/common/boot_control_stub.cc
@@ -59,4 +59,14 @@
   return false;
 }
 
+bool BootControlStub::InitPartitionMetadata(
+    Slot slot, const PartitionSizes& partition_sizes) {
+  LOG(ERROR) << __FUNCTION__ << " should never be called.";
+  return false;
+}
+
+void BootControlStub::Cleanup() {
+  LOG(ERROR) << __FUNCTION__ << " should never be called.";
+}
+
 }  // namespace chromeos_update_engine