Use SkPMColor4f throughout clear APIs

Bug: skia:
Change-Id: I5386e27edbcf39233880d869841a6632ecb9416c
Reviewed-on: https://skia-review.googlesource.com/c/168261
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
diff --git a/src/gpu/ccpr/GrCCAtlas.cpp b/src/gpu/ccpr/GrCCAtlas.cpp
index a566707..0d1f9d9 100644
--- a/src/gpu/ccpr/GrCCAtlas.cpp
+++ b/src/gpu/ccpr/GrCCAtlas.cpp
@@ -202,7 +202,8 @@
     }
 
     SkIRect clearRect = SkIRect::MakeSize(fDrawBounds);
-    rtc->clear(&clearRect, 0, GrRenderTargetContext::CanClearFullscreen::kYes);
+    rtc->clear(&clearRect, SK_PMColor4fTRANSPARENT,
+               GrRenderTargetContext::CanClearFullscreen::kYes);
     return rtc;
 }