Reduce memory used by CompiledMethods.

Use LengthPrefixedArray<>s instead of SwapVector<>s to store
CompiledMethod data and get rid of the unnecessary members
of CompiledMethod to reduce dex2oat memory usage. Refactor
the deduplication from CompilerDriver to a new class.

Use HashSet<> instead of std::set<> for the DedupeSet<> to
further decrease the memory usage and improve performance.

This reduces the dex2oat memory usage when compiling boot
image on Nexus 5 (with Optimizing, -j1) by ~6.75MiB (5%).
This also reduces the compile time by ~2.2% (~1.6% dex2oat
time; with Optimizing, without -j).

Change-Id: I974f1f5e58350de2bf487a2bca3907fa05fb80ea
diff --git a/compiler/linker/arm64/relative_patcher_arm64.cc b/compiler/linker/arm64/relative_patcher_arm64.cc
index 6f234a8..57018af 100644
--- a/compiler/linker/arm64/relative_patcher_arm64.cc
+++ b/compiler/linker/arm64/relative_patcher_arm64.cc
@@ -74,7 +74,7 @@
   // Now that we have the actual offset where the code will be placed, locate the ADRP insns
   // that actually require the thunk.
   uint32_t quick_code_offset = compiled_method->AlignCode(offset) + sizeof(OatQuickMethodHeader);
-  ArrayRef<const uint8_t> code(*compiled_method->GetQuickCode());
+  ArrayRef<const uint8_t> code = compiled_method->GetQuickCode();
   uint32_t thunk_offset = compiled_method->AlignCode(quick_code_offset + code.size());
   DCHECK(compiled_method != nullptr);
   for (const LinkerPatch& patch : compiled_method->GetPatches()) {