1. Run all webkit_unit_tests.
2. Observe that DOMWrapperWorld.Basic always fails the first run.

Failing output:
[355/6925] ActivityLoggerTest.RequestResource (121 ms)                                                 
[ RUN      ] DOMWrapperWorldTest.Basic             
../../third_party/WebKit/Source/bindings/core/v8/DOMWrapperWorldTest.cpp:91: Failure                   
Value of: DOMWrapperWorld::NonMainWorldsExistInMainThread()                                            
  Actual: true           
Expected: false          
../../third_party/WebKit/Source/bindings/core/v8/DOMWrapperWorldTest.cpp:94: Failure                   
      Expected: 1u       
      Which is: 1        
To be equal to: retrieved_worlds.size()            
      Which is: 2        
../../third_party/WebKit/Source/bindings/core/v8/DOMWrapperWorldTest.cpp:137: Failure                  
      Expected: worlds.size() + 1                  
      Which is: 4        
To be equal to: retrieved_worlds.size()            
      Which is: 5        
../../third_party/WebKit/Source/bindings/core/v8/DOMWrapperWorldTest.cpp:146: Failure                  
Value of: DOMWrapperWorld::NonMainWorldsExistInMainThread()                                            
  Actual: true           
Expected: false          
../../third_party/WebKit/Source/bindings/core/v8/DOMWrapperWorldTest.cpp:148: Failure                  
      Expected: 1u       
      Which is: 1        
To be equal to: retrieved_worlds.size()            
      Which is: 2        
[  FAILED  ] DOMWrapperWorldTest.Basic (17 ms)     
[356/6925] DOMWrapperWorldTest.Basic (17 ms)