Log whether user explicitly disabled mixed builds in Soong metrics.

Test: unit tests
Bug: 254649740
Change-Id: I2d4080955e10fe4b50e335c97c79dddbdd22c170
diff --git a/ui/build/config.go b/ui/build/config.go
index cde8d5d..889311d 100644
--- a/ui/build/config.go
+++ b/ui/build/config.go
@@ -464,10 +464,11 @@
 
 func buildConfig(config Config) *smpb.BuildConfig {
 	c := &smpb.BuildConfig{
-		ForceUseGoma:    proto.Bool(config.ForceUseGoma()),
-		UseGoma:         proto.Bool(config.UseGoma()),
-		UseRbe:          proto.Bool(config.UseRBE()),
-		BazelMixedBuild: proto.Bool(config.BazelBuildEnabled()),
+		ForceUseGoma:                proto.Bool(config.ForceUseGoma()),
+		UseGoma:                     proto.Bool(config.UseGoma()),
+		UseRbe:                      proto.Bool(config.UseRBE()),
+		BazelMixedBuild:             proto.Bool(config.BazelBuildEnabled()),
+		ForceDisableBazelMixedBuild: proto.Bool(config.IsBazelMixedBuildForceDisabled()),
 	}
 	c.Targets = append(c.Targets, config.arguments...)
 
@@ -1452,6 +1453,10 @@
 	return c.emptyNinjaFile
 }
 
+func (c *configImpl) IsBazelMixedBuildForceDisabled() bool {
+	return c.Environment().IsEnvTrue("BUILD_BROKEN_DISABLE_BAZEL")
+}
+
 func GetMetricsUploader(topDir string, env *Environment) string {
 	if p, ok := env.Get("METRICS_UPLOADER"); ok {
 		metricsUploader := filepath.Join(topDir, p)