Fix CompilationUnit's UniquePtr usage.

CompilationUnit defined in compiler_ir.h uses UniquePtr with
forward-declared MIRGraph, so the ctor/dtor must be defined
in a compilation unit that actually includes MIRGraph's
definition. Otherwise the build would depend on the order of
includes.

Change-Id: I53096c5f1c975843bad3c375d4ce72a9c0656264
diff --git a/compiler/dex/frontend.cc b/compiler/dex/frontend.cc
index 2f8521f..b8cd67e 100644
--- a/compiler/dex/frontend.cc
+++ b/compiler/dex/frontend.cc
@@ -108,6 +108,38 @@
   // (1 << kDebugTimings) |
   0;
 
+CompilationUnit::CompilationUnit(ArenaPool* pool)
+  : compiler_driver(NULL),
+    class_linker(NULL),
+    dex_file(NULL),
+    class_loader(NULL),
+    class_def_idx(0),
+    method_idx(0),
+    code_item(NULL),
+    access_flags(0),
+    invoke_type(kDirect),
+    shorty(NULL),
+    disable_opt(0),
+    enable_debug(0),
+    verbose(false),
+    compiler_backend(kNoBackend),
+    instruction_set(kNone),
+    num_dalvik_registers(0),
+    insns(NULL),
+    num_ins(0),
+    num_outs(0),
+    num_regs(0),
+    num_compiler_temps(0),
+    compiler_flip_match(false),
+    arena(pool),
+    mir_graph(NULL),
+    cg(NULL),
+    timings("QuickCompiler", true, false) {
+}
+
+CompilationUnit::~CompilationUnit() {
+}
+
 // TODO: Add a cumulative version of logging, and combine with dex2oat --dump-timing
 void CompilationUnit::StartTimingSplit(const char* label) {
   if (enable_debug & (1 << kDebugTimings)) {