Make the Length(LengthType) constructor explicit

Per coding style:

https: //google.github.io/styleguide/cppguide.html#Implicit_Conversions
Change-Id: Ic7a05422e72b3e445236b054d887b5467f79ab6c
Reviewed-on: https://chromium-review.googlesource.com/809010Reviewed-by: Stephen Chenney <schenney@chromium.org>
Commit-Queue: Fredrik Söderquist <fs@opera.com>
Cr-Commit-Position: refs/heads/master@{#521786}

third_party/WebKit/Source/core/style/ComputedStyle.h

@@ -1386,10 +1386,10 @@ class ComputedStyle : public ComputedStyleBase,
            !PaddingTop().IsZero() || !PaddingBottom().IsZero();
   }
   void ResetPadding() {
-    SetPaddingTop(kFixed);
-    SetPaddingBottom(kFixed);
-    SetPaddingLeft(kFixed);
-    SetPaddingRight(kFixed);
+    SetPaddingTop(Length(kFixed));
+    SetPaddingBottom(Length(kFixed));
+    SetPaddingLeft(Length(kFixed));
+    SetPaddingRight(Length(kFixed));
   }
   void SetPadding(const LengthBox& b) {
     SetPaddingTop(b.top_);

third_party/WebKit/Source/platform/Length.h

@@ -64,7 +64,7 @@ class PLATFORM_EXPORT Length {
  public:
   Length() : int_value_(0), quirk_(false), type_(kAuto), is_float_(false) {}
 
-  Length(LengthType t)
+  explicit Length(LengthType t)
       : int_value_(0), quirk_(false), type_(t), is_float_(false) {
     DCHECK_NE(t, kCalculated);
   }