Indexed DB: Ensure large explicit keys consistently max out generator

[chromium-wpt-export-bot]

Background: Stores can have a key generator which generates successive
numeric keys. Storing a record with an explicit numeric key adjusts
they key generator to produce values above the explicit key. Once the
generator hits 2^53 it stops generating new keys (since that's the
maximum integer uniquely representable as a JS number).

Chrome's logic for certain values above this limit was "wonky". Values
above 2^53 would max out the generator. Values above 2^63 and Infinity
would be ignored and not adjust the generator, due to relying on
undefined double->int64_t casting behavior.

Fix to always max out the generator for large values. Also adds
web-platform-tests - other implementations are wonky too. :(

Also adds some missing test coverage for key injection cases.

Spec discussion: w3c/IndexedDB#147

BUG=691754

Review-Url: https://codereview.chromium.org/2735213002
Cr-Commit-Position: refs/heads/master@{#455256}

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[w3c-bots]

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Firefox (nightly channel)

Testing web-platform-tests at revision f457da9
Using browser at version BuildID 20170306110339; SourceStamp 966464a68a2cb3ca1125808e34abb5c1d34e3797
Starting 10 test iterations
All results were stable

All results

2 tests ran

/IndexedDB/keygenerator-explicit.html

Subtest	Results	Messages
	OK
Key generator vs. explicit key 53 bits	PASS
Key generator vs. explicit key greater than 53 bits, less than 64 bits	PASS
Key generator vs. explicit key greater than 53 bits, less than 64 bits (negative)	PASS
Key generator vs. explicit key 63 bits	FAIL	assert_unreached: put should fail Reached unreachable code
Key generator vs. explicit key 63 bits (negative)	PASS
Key generator vs. explicit key 64 bits	FAIL	assert_unreached: put should fail Reached unreachable code
Key generator vs. explicit key 64 bits (negative)	PASS
Key generator vs. explicit key greater than 64 bits, but still finite	FAIL	assert_unreached: put should fail Reached unreachable code
Key generator vs. explicit key greater than 64 bits, but still finite (negative)	PASS
Key generator vs. explicit key equal to Infinity	FAIL	assert_unreached: put should fail Reached unreachable code
Key generator vs. explicit key equal to -Infinity	PASS

/IndexedDB/keygenerator-inject.html

Subtest	Results	Messages
	OK
Key is injected into value - single segment path	PASS
Key is injected into value - multi-segment path	PASS
Key is injected into value - multi-segment path, partially populated	PASS
put() throws if key cannot be injected - single segment path	PASS
put() throws if key cannot be injected - multi-segment path	PASS

[w3c-bots]

View the complete job log.

Chrome (unstable channel)

Testing web-platform-tests at revision f457da9
Using browser at version 58.0.3029.6 dev
Starting 10 test iterations
All results were stable

All results

2 tests ran

/IndexedDB/keygenerator-explicit.html

Subtest	Results	Messages
	OK
Key generator vs. explicit key 53 bits	PASS
Key generator vs. explicit key greater than 53 bits, less than 64 bits	PASS
Key generator vs. explicit key greater than 53 bits, less than 64 bits (negative)	PASS
Key generator vs. explicit key 63 bits	FAIL	assert_unreached: put should fail Reached unreachable code
Key generator vs. explicit key 63 bits (negative)	PASS
Key generator vs. explicit key 64 bits	FAIL	assert_unreached: put should fail Reached unreachable code
Key generator vs. explicit key 64 bits (negative)	PASS
Key generator vs. explicit key greater than 64 bits, but still finite	FAIL	assert_unreached: put should fail Reached unreachable code
Key generator vs. explicit key greater than 64 bits, but still finite (negative)	PASS
Key generator vs. explicit key equal to Infinity	FAIL	assert_unreached: put should fail Reached unreachable code
Key generator vs. explicit key equal to -Infinity	PASS

/IndexedDB/keygenerator-inject.html

Subtest	Results	Messages
	OK
Key is injected into value - single segment path	PASS
Key is injected into value - multi-segment path	PASS
Key is injected into value - multi-segment path, partially populated	PASS
put() throws if key cannot be injected - single segment path	PASS
put() throws if key cannot be injected - multi-segment path	PASS