Better performance for -LayoutUnit

BUG=629932

Review-Url: https://codereview.chromium.org/2171813002
Cr-Commit-Position: refs/heads/master@{#406913}

third_party/WebKit/Source/platform/LayoutUnit.h

@@ -644,12 +644,8 @@ inline float operator-(const float a, const LayoutUnit& b)
 
 inline LayoutUnit operator-(const LayoutUnit& a)
 {
-    // -min() is saturated to max().
-    if (a == LayoutUnit::min())
-        return LayoutUnit::max();
-
     LayoutUnit returnVal;
-    returnVal.setRawValue(-a.rawValue());
+    returnVal.setRawValue(saturatedNegative(a.rawValue()));
     return returnVal;
 }
 

third_party/WebKit/Source/wtf/SaturatedArithmetic.h

@@ -73,6 +73,13 @@ ALWAYS_INLINE int32_t saturatedSubtraction(int32_t a, int32_t b)
     return result;
 }
 
+ALWAYS_INLINE int32_t saturatedNegative(int32_t a)
+{
+    if (UNLIKELY(a == std::numeric_limits<int>::min()))
+        return std::numeric_limits<int>::max();
+    return -a;
+}
+
 inline int getMaxSaturatedSetResultForTesting(int FractionalShift)
 {
     // For C version the set function maxes out to max int, this differs from

third_party/WebKit/Source/wtf/asm/SaturatedArithmeticARM.h

@@ -33,6 +33,11 @@ ALWAYS_INLINE int32_t saturatedSubtraction(int32_t a, int32_t b)
     return result;
 }
 
+ALWAYS_INLINE int32_t saturatedNegative(int32_t a)
+{
+    return saturatedSubtraction(0, a);
+}
+
 inline int getMaxSaturatedSetResultForTesting(int FractionalShift)
 {
     // For ARM Asm version the set function maxes out to the biggest