webkit: Fix ambiguous conversion errors for gcc 4.8

Change-Id: Ifa1a4073a805485a38344a7170ce381e6f0bbbd9
webkit: Update ANGLE library to use the external project

Using the external/angle has bug fix for webgl

Change-Id: I6b519b055d8fcbc30787bb3ea1f0dd4fbc3151cc
CRs-fixed: 427617