ART: Use optimizing compiler in image_test

Expose some compiler options so we can run the image test with
the optimizing compiler without running into a stack overflow.

Also allow a variable amount of threads in CreateCompilerDriver.
Use 16 as a middle ground on the host to speed up the otherwise
now slowed-down test.

Bug: 27240085
Bug: 27552475
Change-Id: I8db5055d32ae722c8f430903244faa9166cc4886
diff --git a/compiler/common_compiler_test.cc b/compiler/common_compiler_test.cc
index 239bc59..6075cd6 100644
--- a/compiler/common_compiler_test.cc
+++ b/compiler/common_compiler_test.cc
@@ -187,7 +187,9 @@
   }
 }
 
-void CommonCompilerTest::CreateCompilerDriver(Compiler::Kind kind, InstructionSet isa) {
+void CommonCompilerTest::CreateCompilerDriver(Compiler::Kind kind,
+                                              InstructionSet isa,
+                                              size_t number_of_threads) {
   compiler_driver_.reset(new CompilerDriver(compiler_options_.get(),
                                             verification_results_.get(),
                                             method_inliner_map_.get(),
@@ -198,7 +200,7 @@
                                             GetImageClasses(),
                                             GetCompiledClasses(),
                                             GetCompiledMethods(),
-                                            /* thread_count */ 2,
+                                            number_of_threads,
                                             /* dump_stats */ true,
                                             /* dump_passes */ true,
                                             timer_.get(),