Automated g4 rollback of changelist 67187838.

*** Reason for rollback ***

Breaks builds.

*** Original change description ***

Update the externs for Notification so that "window.Notification" and "Notification" have the same type.

***
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Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=67197538
Disable threads in TemplateAstMatcherTest
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Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=67265813
Transpile class expressions and class declarations from ES6 to ES3.

Not all classes are supported yet; see #419

Fixes #418
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Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=67269493
Test fix to enable DeclaredGlobalExternsOnWindow to be enabled.
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Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=67283078