Fixes issue #488
Add a parser test for unterminated string literals.
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Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=69309054
[NEW TYPE INFERENCE] Don't include free variables in FunctionType.toString
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Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=69313416
[NEW TYPE INFERENCE] Allocate fewer types in JSType.substituteGenerics
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Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=69330329
Add chrome.webstore API to common chrome_extensions externs.

This also removes the duplicate definitions in project-specific externs files.
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Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=69335839
Makes JSMessageVisitor take source mappings into account.
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Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=69365366
Don't rewrite undefined to window.undefined in RescopeGlobalSymbols.
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Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=69383811
Tigthten the return type of a few methods.
Fixes github issue 488
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Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=69385393
Merge pull request #491 from retromodular/patch-488

Fixes issue #488