ART: PathClassLoader for compiler

Use an actual PathClassLoader when compiling apps, instead of a
side structure and cutout.

This CL sets up a minimal object 'cluster' that recreates the Java
side of a regular ClassLoader such that the Class-Linker will
recognize it and use the internal native fast-path.

This CL removes the now unnecessary compile-time-classpath and
replaces it with a single 'compiling-the-boot-image' flag in the
compiler callbacks.

Note: This functionality is *only* intended for the compiler, as
the objects have not been completely initialized.

Bug: 19781184

Change-Id: I7f36af12dd7852d21281110a25c119e8c0669c1d
diff --git a/runtime/compiler_callbacks.h b/runtime/compiler_callbacks.h
index d1a6861..3fabe3e 100644
--- a/runtime/compiler_callbacks.h
+++ b/runtime/compiler_callbacks.h
@@ -40,8 +40,16 @@
     // done so. Return false if relocating in this way would be problematic.
     virtual bool IsRelocationPossible() = 0;
 
+    bool IsBootImage() {
+      return boot_image_;
+    }
+
   protected:
-    CompilerCallbacks() { }
+    explicit CompilerCallbacks(bool boot_image) : boot_image_(boot_image) { }
+
+  private:
+    // Whether the compiler is creating a boot image.
+    const bool boot_image_;
 };
 
 }  // namespace art