fix(numberFilter): correctly round fractions despite floating-point arithmetics issues in JS

Closes angular#7870
Closes angular#7878

Author: IgorMinar

src/ng/filter/filters.js

@@ -145,8 +145,11 @@ function formatNumber(number, pattern, groupSep, decimalSep, fractionSize) {
       fractionSize = Math.min(Math.max(pattern.minFrac, fractionLen), pattern.maxFrac);
     }
 
-    var pow = Math.pow(10, fractionSize + 1);
-    number = Math.floor(number * pow + 5) / pow;
+    // safely round numbers in JS without hitting imprecisions of floating-point arithmetics
+    // inspired by:
+    // https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Math/round
+    number = +(Math.round(+(number.toString() + 'e' + fractionSize)).toString() + 'e' + -fractionSize);
+
     var fraction = ('' + number).split(DECIMAL_SEP);
     var whole = fraction[0];
     fraction = fraction[1] || '';

test/ng/filter/filtersSpec.js

@@ -147,13 +147,18 @@ describe('filters', function() {
       expect(number(.99,      2)).toEqual("0.99");
       expect(number(.999,     3)).toEqual("0.999");
       expect(number(.9999,    3)).toEqual("1.000");
+      expect(number(1.9,      2)).toEqual("1.90");
+      expect(number(1.99,     2)).toEqual("1.99");
+      expect(number(1.999,    3)).toEqual("1.999");
+      expect(number(1.9999,   3)).toEqual("2.000");
       expect(number(1234.567, 0)).toEqual("1,235");
       expect(number(1234.567, 1)).toEqual("1,234.6");
       expect(number(1234.567, 2)).toEqual("1,234.57");
       expect(number(1.255,    0)).toEqual("1");
       expect(number(1.255,    1)).toEqual("1.3");
       expect(number(1.255,    2)).toEqual("1.26");
       expect(number(1.255,    3)).toEqual("1.255");
+      expect(number(0,        8)).toEqual("0.00000000");
     });
 
     it('should filter exponentially large numbers', function() {