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

tools/clang/blink_gc_plugin/BlinkGCPlugin.cpp

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // This clang plugin checks various invariants of the Blink garbage
 // collection infrastructure.
 //
 // Errors are described at:
 // http://www.chromium.org/developers/blink-gc-plugin-errors
 
@@ skipping 843 matching lines @@
         DiagnosticsEngine::Note, kBaseRequiresFinalizationNote);
     diag_field_requires_finalization_note_ = diagnostic_.getCustomDiagID(
         DiagnosticsEngine::Note, kFieldRequiresFinalizationNote);
     diag_overridden_non_virtual_trace_note_ = diagnostic_.getCustomDiagID(
         DiagnosticsEngine::Note, kOverriddenNonVirtualTraceNote);
     diag_manual_dispatch_method_note_ = diagnostic_.getCustomDiagID(
         DiagnosticsEngine::Note, kManualDispatchMethodNote);
   }
 
   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());
 
     if (options_.dump_graph) {
       std::error_code err;
       // TODO: Make createDefaultOutputFile or a shorter createOutputFile work.
       json_ = JsonWriter::from(instance_.createOutputFile(
           "",                                      // OutputPath
           err,                                     // Errors
           true,                                    // Binary
@@ skipping 1001 matching lines @@
 
  private:
   BlinkGCPluginOptions options_;
 };
 
 }  // namespace
 
 static FrontendPluginRegistry::Add<BlinkGCPluginAction> X(
     "blink-gc-plugin",
     "Check Blink GC invariants");