Exclude targets depending on sqlite from embedder builds

In embedder builds (e.g. V8) sqlite is not available, which results in
errors when perfetto build files are included. This CL hides all sqlite
stuff behind a flag.

Change-Id: Ibe79344e609244b459d5705b05295e26f8b93db4
diff --git a/gn/perfetto_unittests.gni b/gn/perfetto_unittests.gni
index ead0c8b..11ba49f 100644
--- a/gn/perfetto_unittests.gni
+++ b/gn/perfetto_unittests.gni
@@ -61,8 +61,9 @@
 }
 
 if (enable_perfetto_trace_processor) {
-  perfetto_unittests_targets += [
-    "src/trace_processor:unittests",
-    "src/trace_processor/metrics:unittests",
-  ]
+  perfetto_unittests_targets += [ "src/trace_processor:unittests" ]
+
+  if (enable_perfetto_trace_processor_sqlite) {
+    perfetto_unittests_targets += [ "src/trace_processor/metrics:unittests" ]
+  }
 }