Reland of [sensors] Ambient light sensor bindings implementation

Reverted in:
https://codereview.chromium.org/2348333002/

Reason for revert:
Two new tests are failing on several Blink bots.

Original CL: https://codereview.chromium.org/2332323002/

This patch implements AmbientLightSensor [1] blink bindings and adds
LayoutTest helpers for testing sensors that are based on Generic Sensor API.

Following layout tests added to test new functionality:
IDL tests.
- third_party/WebKit/LayoutTests/sensor/idl-AmbientLightSensor.html
AmbientLightSensor tests.
- third_party/WebKit/LayoutTests/sensor/ambient-light-sensor.html

Intent to Implement:
https://groups.google.com/a/chromium.org/forum/#!msg/blink-dev/TkfdVqYAYiE/xLGN2b1-AAAJ

[1] ED specification for Ambient Light Sensor http://w3c.github.io/ambient-light/

TBR=haraken@chromium.org,jochen@chromium.org,timvolodine@chromium.org,mikhail.pozdnyakov@intel.com
BUG=606766

Review-Url: https://codereview.chromium.org/2356133002
Cr-Commit-Position: refs/heads/master@{#421484}
16 files changed