Revert of Revert of use gradient API that skips (deprecated) unitmapper param (https://codereview.chromium.org/295583007/)

Reason for revert:
Local sync problem.

Original issue's description:
> Revert of use gradient API that skips (deprecated) unitmapper param (https://codereview.chromium.org/293703003/)
> 
> Reason for revert:
> Broke the build
> 
> ../../third_party/WebKit/Source/platform/graphics/Gradient.cpp:247:147: error: cannot initialize a parameter of type 'SkUnitMapper *' with an lvalue of type 'uint32_t' (aka 'unsigned int')
>             m_gradient = adoptRef(SkGradientShader::CreateRadial(m_p1.data(), m_r1, colors.data(), pos.data(), static_cast<int>(countUsed), tile, shouldDrawInPMColorSpace, &localMatrix));
> 
> 
> Original issue's description:
> > use gradient API that skips (deprecated) unitmapper param
> > 
> > NOTRY=True
> > 
> > Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=174497
> 
> TBR=fmalita@chromium.org,schenney@chromium.org,reed@chromium.org,reed@google.com
> NOTREECHECKS=true
> NOTRY=true
> 
> Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=174507

TBR=schenney@chromium.org,reed@chromium.org,reed@google.com,esprehn@chromium.org
NOTREECHECKS=true
NOTRY=true

Review URL: https://codereview.chromium.org/284183010

git-svn-id: svn://svn.chromium.org/blink/trunk@174519 bbb929c8-8fbe-4397-9dbb-9b2b20218538