add more checks for computing clamp counts, remove dead code

src/effects/gradients/SkClampRange.cpp

Index: src/effects/gradients/SkClampRange.cpp
diff --git a/src/effects/gradients/SkClampRange.cpp b/src/effects/gradients/SkClampRange.cpp
index 4f8611281a30607376eb63b227f2809120d2e553..061016432ffefcc2e64322054a440c0a74848490 100644
--- a/src/effects/gradients/SkClampRange.cpp
+++ b/src/effects/gradients/SkClampRange.cpp
@@ -77,8 +77,6 @@ void SkClampRange::init(SkGradFixed fx0, SkGradFixed dx0, int count, int v0, int
         return;
     }
 
-    int extraCount = 0;
-
     // now make ex be 1 past the last computed value
     ex += dx;
 
@@ -93,11 +91,15 @@ void SkClampRange::init(SkGradFixed fx0, SkGradFixed dx0, int count, int v0, int
 
 
     fCount0 = chop(fx, 0, ex, dx, count);
+    SkASSERT(fCount0 >= 0);
+    SkASSERT(fCount0 <= count);
     count -= fCount0;
     fx += fCount0 * dx;
     SkASSERT(fx >= 0);
     SkASSERT(fCount0 == 0 || (fx - dx) < 0);
     fCount1 = chop(fx, kFracMax_SkGradFixed, ex, dx, count);
+    SkASSERT(fCount1 >= 0);
+    SkASSERT(fCount1 <= count);
     count -= fCount1;
     fCount2 = count;
 
@@ -121,10 +123,4 @@ void SkClampRange::init(SkGradFixed fx0, SkGradFixed dx0, int count, int v0, int
     if (fCount1 > 0) {
         fFx1 = fx0 + fCount0 * dx;
     }
-
-    if (dx > 0) {
-        fCount2 += extraCount;
-    } else {
-        fCount0 += extraCount;
-    }
 }