Make ignorewarnings optional in optimize

This allows targets to opt-in to running R8 without the -ignorewarnings
flag. Ignored warnings can cause code to be optimized incorrectly, so
this makes the build safer for such targets.

Ideally ignore_warnings should default to false, but all targets need to
be fixed for that to happen. As a first step, provide a mechanism for
individual targets to ensure they do not introduce regressions.

Bug: 229727645
Bug: 180878971
Bug: 226127213
Bug: 239990030
Test: m (runs dex_test)
Change-Id: Ic0eef29598c1ee47e958da8a5048d9696165a235

java/dex_test.go

@@ -59,6 +59,36 @@ func TestR8(t *testing.T) {
 		appR8.Args["r8Flags"], libHeader.String())
 	android.AssertStringDoesNotContain(t, "expected no  static_lib header jar in app javac classpath",
 		appR8.Args["r8Flags"], staticLibHeader.String())
+	android.AssertStringDoesContain(t, "expected -ignorewarnings in app r8 flags",
+		appR8.Args["r8Flags"], "-ignorewarnings")
+}
+
+func TestR8Flags(t *testing.T) {
+	result := PrepareForTestWithJavaDefaultModulesWithoutFakeDex2oatd.RunTestWithBp(t, `
+		android_app {
+			name: "app",
+			srcs: ["foo.java"],
+			platform_apis: true,
+			optimize: {
+				shrink: false,
+				optimize: false,
+				obfuscate: false,
+				ignore_warnings: false,
+			},
+		}
+	`)
+
+	app := result.ModuleForTests("app", "android_common")
+	appR8 := app.Rule("r8")
+	android.AssertStringDoesContain(t, "expected -dontshrink in app r8 flags",
+		appR8.Args["r8Flags"], "-dontshrink")
+	android.AssertStringDoesContain(t, "expected -dontoptimize in app r8 flags",
+		appR8.Args["r8Flags"], "-dontoptimize")
+	android.AssertStringDoesContain(t, "expected -dontobfuscate in app r8 flags",
+		appR8.Args["r8Flags"], "-dontobfuscate")
+	android.AssertStringDoesNotContain(t, "expected no -ignorewarnings in app r8 flags",
+		appR8.Args["r8Flags"], "-ignorewarnings")
+
 }
 
 func TestD8(t *testing.T) {