Make return types non-nullable on functions which never return null.

Cleanup change initially generated by JsFlume Refactoring: See cl/64107256

After running the refactoring, I manually fixed a few cases which the refactoring gets wrong, and reverted cases where the JsDoc explicitly says the function may return null. If one of the changes still looks wrong, please use go/suggestfix to fix or revert it.

Tested:
TAP presubmits for global presubmit queue
http://test/OCL:64145361:BASE:64368061:1396632582166:c5b1e185
Some tests failed; test failures are believed to be unrelated to this CL
-------------
Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=64380389
Make return types non-nullable on functions which never return null.

Cleanup change initially generated by JsFlume Refactoring: See cl/64107256

After running the refactoring, I manually fixed a few cases which the refactoring gets wrong, and reverted cases where the JsDoc explicitly says the function may return null. If one of the changes still looks wrong, please use go/suggestfix to fix or revert it.

Tested:
TAP presubmits for global presubmit queue
http://test/OCL:64145377:BASE:64273715:1396519296046:85d7c329
Some tests failed; test failures are believed to be unrelated to this CL
-------------
Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=64492722
Remove Firefox 2 hack for -moz-box-orient in goog.ui.CustomButton and
apps.ui.Marquee CSS.
-------------
Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=64510569
Add a test to verify that \ gets percent-encoded. Since this is a somewhat dangerous character we really want to be sure.
-------------
Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=64540452
Fix incorrect documentation link.
-------------
Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=64549909
use goog.array in closure.labs.html instead of [].lastIndexOf which IE7 lacks

The tests
//javascript/closure:jstests_5_ie7-winxp
//javascript/closure:jstests_5_ie8-winxp
failed because IE 7 and IE 8 do not support Array,prototype.lastIndexOf

For reference:

http://kangax.github.io/es5-compat-table/#Array.prototype.lastIndexOf

This CL also re-enables tests that were disabled in CL 64219012 by useragent
checking.
-------------
Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=64556197
Removed test HTML file added in CL 63419243

gboyer explains:
> I am so trained to accepting HTML tests that I didn't think about it.
> You're supposed to run javascript/closure:jstests_#_debug and go to
> localhost:4000.
-------------
Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=64559905
Update type annotation for slider's label function to correctly allow it to return null.
-------------
Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=64640991
Fix typo in //javascript/closure/html/safeurl.js.
-------------
Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=64641564
Update the return type of goog.userAgent.getUserAgentString to indicate that it
can never return null anymore.
-------------
Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=64666070
Remove IE5 code in goog.dom.getOwnerDocument since it's 2014.
-------------
Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=64709268
Add goog.json.USE_NATIVE_JSON check to goog.json.hybrid.
-------------
Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=64715211
Automated g4 rollback of changelist 64709268.

*** Reason for rollback ***

breaking various targets because null is not supported

*** Original change description ***

Remove IE5 code in goog.dom.getOwnerDocument since it's 2014.

***
-------------
Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=64718901
Make goog.testing.TestCase.MAX_RUN_TIME settable.

When running tests in embedded v8, there's no need to cycle tests asynchronously.
-------------
Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=64752013
Fixing bug where goog.style.getFontFamily would fail with 'Invalid argument' if provided element is not attached to the document.
-------------
Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=64802496
On Android webkits something in unit tests sometimes calls this after tearDown when the clock has already been disposed, leading to flaky errors.
-------------
Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=64804300
Make return types non-nullable on functions which never return null.

This CL was created by running the "nullable return" refactoring on //

More information: go/lsc-nullable-return

ATTENTION REVIEWERS: This refactoring is not perfect so please review the changes carefully and use go/suggestfix if anything looks suspicious. For example, {Foo|Bar} will be replaced with {!Foo|Bar} whereas it should be {!Foo|!Bar}

Tested:
TAP presubmits for global presubmit queue
http://test/OCL:64662798:BASE:64784688:1397238091890:800d2306
Some tests failed; test failures are believed to be unrelated to this CL
-------------
Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=64808643
Make return types non-nullable on functions which never return null.

More information: go/lsc-nullable-return

ATTENTION REVIEWERS: This refactoring is not perfect so please review the changes carefully and use go/suggestfix if anything looks suspicious. For example, {Foo|Bar} will be replaced with {!Foo|Bar} whereas it should be {!Foo|!Bar}

Tested:
TAP presubmits for global presubmit queue
http://test/OCL:64662473:BASE:64790945:1397243100976:1fd14581
Some tests failed; test failures are believed to be unrelated to this CL
-------------
Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=64809190
Performance optimization.  Reduce the number of double<->integer
conversions by adding bit masks and using typed arrays.  Improves
Chrome and Firefox perf test performance by 10-20%.  A test of
Closure-compiled code of a large string improved 20-30% on both
Chrome and Firefox.
-------------
Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=64821551
Don't depend on the value of the global variable 'undefined'. Uses `void 0` instead which /always/ evaluates to undefined.
-------------
Created by MOE: http://code.google.com/p/moe-java
MOE_MIGRATED_REVID=64905380