[WebViewLayoutTest] Fix potential rounding error in testBatteryApi() layout test.

[WebViewLayoutTest] Fix potential rounding error in testBatteryApi() layout test.

The battery.level precision test isInteger(battery.level * 100) can
occasionally fail due to rounding error,
e.g. (0.58 * 100) % 1 = 0.9999999999999929.
This patch uses toPrecision and toString methods instead to correct
this issue.

BUG=

Committed: https://crrev.com/beebf8aac8acd93bd045d94a5835e12b4992176e
Cr-Commit-Position: refs/heads/master@{#354498}

Committed: https://crrev.com/863fd741f32361a9154a61482e29944befe767ca
Cr-Commit-Position: refs/heads/master@{#354533}

[timvolodine, 2015-10-14 15:44:33]

timvolodine@chromium.org changed reviewers:
+ mvanouwerkerk@chromium.org

[Michael van Ouwerkerk, 2015-10-15 14:57:00]

lgtm

[timvolodine, 2015-10-16 12:14:20]

The CQ bit was checked by timvolodine@chromium.org

[commit-bot: I haz the power, 2015-10-16 12:14:47]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1394303007/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1394303007/1

[commit-bot: I haz the power, 2015-10-16 12:25:37]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-10-16 12:26:14]

Patchset 1 (id:??) landed as
https://crrev.com/beebf8aac8acd93bd045d94a5835e12b4992176e
Cr-Commit-Position: refs/heads/master@{#354498}

[johnme, 2015-10-16 14:00:49]

A revert of this CL (patchset #1 id:1) has been created in
https://codereview.chromium.org/1406243002/ by johnme@chromium.org.

The reason for reverting is: This patch caused WebViewLayoutTest#testBatteryApi
to fail consistently on
https://uberchromegw.corp.google.com/i/chromium.android/builders/Android%20We...
onwards..

[timvolodine, 2015-10-16 16:58:38]

The CQ bit was checked by timvolodine@chromium.org

[timvolodine, 2015-10-16 16:58:38]

The patchset sent to the CQ was uploaded after l-g-t-m from
mvanouwerkerk@chromium.org
Link to the patchset: https://codereview.chromium.org/1394303007/#ps20001
(title: "fix the precision test")

[commit-bot: I haz the power, 2015-10-16 16:58:56]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1394303007/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1394303007/20001

[commit-bot: I haz the power, 2015-10-16 17:09:39]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-10-16 17:10:51]

Patchset 2 (id:??) landed as
https://crrev.com/863fd741f32361a9154a61482e29944befe767ca
Cr-Commit-Position: refs/heads/master@{#354533}