Rewrite image type in CompilerOptions.

Prepare for introduction of boot image extension.

Test: m test-art-host-gtest
Test: testrunner.py --host --optimizing
Test: Pixel 2 XL boots.
Change-Id: Id007c4aeb4ada84fe65c1148fdf67e8a412e5b74
diff --git a/compiler/common_compiler_test.cc b/compiler/common_compiler_test.cc
index 599f4aa..66421e2 100644
--- a/compiler/common_compiler_test.cc
+++ b/compiler/common_compiler_test.cc
@@ -184,7 +184,7 @@
 void CommonCompilerTest::CreateCompilerDriver() {
   ApplyInstructionSet();
 
-  compiler_options_->boot_image_ = true;
+  compiler_options_->image_type_ = CompilerOptions::ImageType::kBootImage;
   compiler_options_->compile_pic_ = false;  // Non-PIC boot image is a test configuration.
   compiler_options_->SetCompilerFilter(GetCompilerFilter());
   compiler_options_->image_classes_.swap(*GetImageClasses());
@@ -345,7 +345,7 @@
 }
 
 void CommonCompilerTest::ClearBootImageOption() {
-  compiler_options_->boot_image_ = false;
+  compiler_options_->image_type_ = CompilerOptions::ImageType::kNone;
 }
 
 }  // namespace art