Only look for profiles when we have a profile dir

Right now, it's looking for *.prof files at the top of the source
directory.

For devices that don't specify the profile dir (everything on AOSP,
etc), this saves a couple percent of the globs that we check during
every build (and would re-execute if you add or remove files from the
top directory)

Bug: 159845846
Test: treehugger
Change-Id: I10d43422a2b5ae25e6557d435ecc89fe43536dd7

java/dexpreopt.go

@@ -173,7 +173,7 @@ func (d *dexpreopter) dexpreopt(ctx android.ModuleContext, dexJarFile android.Mo
 			profileBootListing = android.ExistentPathForSource(ctx,
 				ctx.ModuleDir(), String(d.dexpreoptProperties.Dex_preopt.Profile)+"-boot")
 			profileIsTextListing = true
-		} else {
+		} else if global.ProfileDir != "" {
 			profileClassListing = android.ExistentPathForSource(ctx,
 				global.ProfileDir, ctx.ModuleName()+".prof")
 		}