Make blink::LayoutUnit::HasFraction constexpr

Other HasFraction methods as in PhysicalUnit are declared already
constexpr and using it. It breaks GCC build.

Bug: 819294.
Change-Id: I0c4bd9bd206d45cf31f7fa815ce8533718a425cb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1645222Reviewed-by: vmpstr <vmpstr@chromium.org>
Reviewed-by: Xianzhu Wang <wangxianzhu@chromium.org>
Commit-Queue: José Dapena Paz <jose.dapena@lge.com>
Cr-Commit-Position: refs/heads/master@{#666336}

third_party/blink/renderer/platform/geometry/layout_unit.h

@@ -202,7 +202,9 @@ class LayoutUnit {
     return value_ > 0 ? LayoutUnit() : *this;
   }
 
-  bool HasFraction() const { return RawValue() % kFixedPointDenominator; }
+  constexpr bool HasFraction() const {
+    return RawValue() % kFixedPointDenominator;
+  }
 
   LayoutUnit Fraction() const {
     // Compute fraction using the mod operator to preserve the sign of the value