fix WBMP image will get null color table when draw in RGB565 Canvas

fix WBMP image will get null color table when draw in RGB565 Canvas

Symptom: draw Index8 to RGB565 will using SkColorTable::lock16BitCache and return a null array.
Root Cause:lock16BitCache return null pointer because default type is kPremul_SkAlphaType
Solution: WBMP color table should be kOpaque_SkAlphaType
Reproduce steps: draw a WBMP with a matrix that apply rotate and transform

This patch was proposed by arthur_hung at htc.com to the AOSP project.

R=reed@google.com, scroggo@google.com

Committed: https://skia.googlesource.com/skia/+/56a6b6b

[reed1, 2014-07-07 14:28:58]

lgtm

[scroggo, 2014-07-07 14:31:11]

On 2014/07/07 14:28:58, reed1 wrote:
> lgtm

lgtm

[djsollen, 2014-07-08 12:23:36]

Committed patchset #1 manually as r56a6b6b (presubmit successful).