Refactor space bitmap to support different alignments.

Required for:
Using space bitmaps instead of std::set in mod union table +
remembered set.
Using a bitmap instead of set for large object marking.

Bug: 13571028

Change-Id: Id024e9563d4ca4278f79607cdb2f81895121b113
diff --git a/compiler/image_writer.cc b/compiler/image_writer.cc
index 0405198..f76587a 100644
--- a/compiler/image_writer.cc
+++ b/compiler/image_writer.cc
@@ -235,8 +235,8 @@
   }
 
   // Create the image bitmap.
-  image_bitmap_.reset(gc::accounting::SpaceBitmap::Create("image bitmap", image_->Begin(),
-                                                          length));
+  image_bitmap_.reset(gc::accounting::ContinuousSpaceBitmap::Create("image bitmap", image_->Begin(),
+                                                                    length));
   if (image_bitmap_.get() == nullptr) {
     LOG(ERROR) << "Failed to allocate memory for image bitmap";
     return false;
@@ -525,7 +525,7 @@
 
   // Return to write header at start of image with future location of image_roots. At this point,
   // image_end_ is the size of the image (excluding bitmaps).
-  const size_t heap_bytes_per_bitmap_byte = kBitsPerByte * gc::accounting::SpaceBitmap::kAlignment;
+  const size_t heap_bytes_per_bitmap_byte = kBitsPerByte * kObjectAlignment;
   const size_t bitmap_bytes = RoundUp(image_end_, heap_bytes_per_bitmap_byte) /
       heap_bytes_per_bitmap_byte;
   ImageHeader image_header(PointerToLowMemUInt32(image_begin_),