Blink GC plugin: Don't check conditions on invalid compilation units.

tools/clang/blink_gc_plugin/BlinkGCPlugin.cpp

Index: tools/clang/blink_gc_plugin/BlinkGCPlugin.cpp
diff --git a/tools/clang/blink_gc_plugin/BlinkGCPlugin.cpp b/tools/clang/blink_gc_plugin/BlinkGCPlugin.cpp
index 8658b04304f32cba63509a9a7fd97df2ba63f1d3..59cd41735a6e6572b6c56552e310a93b20e05a8e 100644
--- a/tools/clang/blink_gc_plugin/BlinkGCPlugin.cpp
+++ b/tools/clang/blink_gc_plugin/BlinkGCPlugin.cpp
@@ -861,6 +861,10 @@ class BlinkGCPluginConsumer : public ASTConsumer {
   }
 
   void HandleTranslationUnit(ASTContext& context) override {
+    // Don't run the plugin if the compilation unit is already invalid.
+    if (diagnostic_.hasErrorOccurred())
+      return;
+
     CollectVisitor visitor;
     visitor.TraverseDecl(context.getTranslationUnitDecl());