COLGROUP / COL: Setting |span| IDL value should reflect to |span| attribute as is.

We don't need a special handling for 0 value.

https://html.spec.whatwg.org/multipage/common-dom-interfaces.html#clamped-to-the-range
> On setting, it behaves the same as setting a regular reflected unsigned integer.

Bug: 745376
Change-Id: I6dead5b474324cd19e811c950971e5804532508a
Reviewed-on: https://chromium-review.googlesource.com/575738Reviewed-by: Takayoshi Kochi <kochi@chromium.org>
Commit-Queue: Kent Tamura <tkent@chromium.org>
Cr-Commit-Position: refs/heads/master@{#487445}

third_party/WebKit/LayoutTests/external/wpt/html/dom/reflection-tabular-expected.txt

@@ -32,10 +32,7 @@ PASS colgroup.accessKey: 32 tests
 PASS colgroup.tabIndex: 24 tests
 PASS colgroup.span: 11 tests
 FAIL colgroup.span: setAttribute() to 4294967296 assert_equals: IDL get expected 1000 but got 1
-PASS colgroup.span: 44 tests
-FAIL colgroup.span: IDL set to 0 assert_equals: getAttribute() expected "0" but got "1"
-PASS colgroup.span: 3 tests
-FAIL colgroup.span: IDL set to "-0" assert_equals: getAttribute() expected "0" but got "1"
+PASS colgroup.span: 49 tests
 FAIL colgroup.span: IDL set to 2147483648 assert_equals: getAttribute() expected "1" but got "0"
 FAIL colgroup.span: IDL set to 4294967295 assert_equals: getAttribute() expected "1" but got "0"
 PASS colgroup.span: 2 tests
@@ -53,10 +50,7 @@ PASS col.accessKey: 32 tests
 PASS col.tabIndex: 24 tests
 PASS col.span: 11 tests
 FAIL col.span: setAttribute() to 4294967296 assert_equals: IDL get expected 1000 but got 1
-PASS col.span: 44 tests
-FAIL col.span: IDL set to 0 assert_equals: getAttribute() expected "0" but got "1"
-PASS col.span: 3 tests
-FAIL col.span: IDL set to "-0" assert_equals: getAttribute() expected "0" but got "1"
+PASS col.span: 49 tests
 FAIL col.span: IDL set to 2147483648 assert_equals: getAttribute() expected "1" but got "0"
 FAIL col.span: IDL set to 4294967295 assert_equals: getAttribute() expected "1" but got "0"
 PASS col.span: 2 tests

third_party/WebKit/Source/core/html/HTMLTableColElement.cpp

@@ -100,7 +100,7 @@ HTMLTableColElement::AdditionalPresentationAttributeStyle() {
 }
 
 void HTMLTableColElement::setSpan(unsigned n) {
-  SetUnsignedIntegralAttribute(spanAttr, n ? n : 1);
+  SetUnsignedIntegralAttribute(spanAttr, n);
 }
 
 const AtomicString& HTMLTableColElement::Width() const {