Revert "Revert "Enable Skia's new linear gradient impl for 8888""

This reverts commit a402d5e0.

Reason for revert: not the cause for the form flakes (https://crbug.com/761070)

Original change's description:
> Revert "Enable Skia's new linear gradient impl for 8888"
> 
> This reverts commit 8d388ccf.
> 
> Reason for revert:
> Sorry to revert such a large CL, but I believe it to be the culprit of
> many calendar-picker flaky failures on Mac10.11:
> https://uberchromegw.corp.google.com/i/chromium.webkit/builders/WebKit%20Mac10.11?numbuilds=200
> 
> Initial failures:
> https://uberchromegw.corp.google.com/i/chromium.webkit/builders/WebKit%20Mac10.11/builds/23036
> 
> Unexpected Failures:
> * fast/forms/calendar-picker/calendar-picker-appearance-zoom125.html
> * fast/forms/calendar-picker/calendar-picker-datetimelocal.html
> * fast/forms/calendar-picker/calendar-picker-key-operations.html
> * fast/forms/calendar-picker/calendar-picker-pre-100-year.html
> * fast/forms/calendar-picker/calendar-picker-should-not-change-datetimelocal-time.html
> * fast/forms/calendar-picker/date-picker-choose-default-value-after-set-value.html
> * fast/forms/calendar-picker/datetimelocal-picker-choose-default-value-after-set-value.html
> * fast/forms/calendar-picker/week-picker-choose-default-value-after-set-value.html
> * fast/forms/calendar-picker/week-picker-mouse-operations.html
> * fast/forms/color/color-suggestion-picker-appearance-zoom200.html
> * fast/forms/suggestion-picker/date-suggestion-picker-appearance-with-scroll-bar.html
> * fast/forms/suggestion-picker/date-suggestion-picker-appearance.html
> * fast/forms/suggestion-picker/date-suggestion-picker-key-operations.html
> * fast/forms/suggestion-picker/datetimelocal-suggestion-picker-appearance-with-scroll-bar.html
> * fast/forms/suggestion-picker/datetimelocal-suggestion-picker-appearance.html
> * fast/forms/suggestion-picker/datetimelocal-suggestion-picker-key-operations.html
> * fast/forms/suggestion-picker/month-suggestion-picker-appearance-with-scroll-bar.html
> * fast/forms/suggestion-picker/month-suggestion-picker-key-operations.html
> * fast/forms/suggestion-picker/time-suggestion-picker-appearance-locale-hebrew.html
> * fast/forms/suggestion-picker/time-suggestion-picker-key-operations.html
> * fast/forms/suggestion-picker/week-suggestion-picker-appearance-with-scroll-bar.html
> * fast/forms/suggestion-picker/week-suggestion-picker-appearance.html
> * fast/forms/suggestion-picker/week-suggestion-picker-key-operations.html
> 
> Original change's description:
> > Enable Skia's new linear gradient impl for 8888
> > 
> > (remove SK_SUPPORT_LEGACY_LINEAR_GRADIENT)
> > 
> > The new implementation is generally more correct/accurate, slightly
> > faster in some cases and slightly slower in others.
> > 
> > TBR=
> > 
> > Change-Id: If1fd4115b40602491b8535e4a9a1cce7855d4209
> > Reviewed-on: https://chromium-review.googlesource.com/642368
> > Commit-Queue: Florin Malita <fmalita@chromium.org>
> > Reviewed-by: Mike Klein <mtklein@chromium.org>
> > Reviewed-by: Florin Malita <fmalita@chromium.org>
> > Cr-Commit-Position: refs/heads/master@{#498619}
> 
> TBR=fmalita@chromium.org,reed@chromium.org,mtklein@chromium.org
> 
> Change-Id: Ic4d9ae1a43a2e62dc48a8d69f72701e8c7d62e94
> No-Presubmit: true
> No-Tree-Checks: true
> No-Try: true
> Reviewed-on: https://chromium-review.googlesource.com/646086
> Reviewed-by: Henrik Boström <hbos@chromium.org>
> Commit-Queue: Henrik Boström <hbos@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#498851}

TBR=fmalita@chromium.org,reed@chromium.org,hbos@chromium.org,mtklein@chromium.org

Change-Id: I6d0b52355599bd8afb78266ab68b9dc6a35c0be5
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/646606Reviewed-by: Florin Malita <fmalita@chromium.org>
Commit-Queue: Florin Malita <fmalita@chromium.org>
Cr-Commit-Position: refs/heads/master@{#498931}

skia/config/SkUserConfig.h

@@ -204,10 +204,6 @@ SK_API void SkDebugf_FileLine(const char* file, int line, bool fatal,
 #   define SK_USE_LEGACY_DISTANCE_FIELDS
 #endif
 
-#ifndef SK_SUPPORT_LEGACY_LINEAR_GRADIENT
-#define SK_SUPPORT_LEGACY_LINEAR_GRADIENT
-#endif
-
 #ifndef SK_SUPPORT_LEGACY_STREAM_API
 #define SK_SUPPORT_LEGACY_STREAM_API
 #endif