fix(compile): do not watch constant media attributes

By creating attribute directives that watch the value of
media url attributes (e.g. `img[src]`) we caused a conflict
when both `src` and `data-src` were appearing on the
same element. As each directive was trying to write to the
attributes on the element, where AngularJS treats `src` and
`data-src` as synonymous.

This commit ensures that we do not create watchers when
the media url attribute is a constant (no interpolation).

Fixes #16734

Author: petebacondarwin

src/ng/compile.js

@@ -3871,6 +3871,12 @@ function $CompileProvider($provide, $$sanitizeUriProvider) {
         compile: function() {
             return {
               pre: function attrInterpolatePreLinkFn(scope, element, attr) {
+                if (trustedContext === $sce.MEDIA_URL && isConstantInterpolation(interpolateFn)) {
+                  // Constant MEDIA_URL attributes should just be sanitized and not watched.
+                  attr[name] = interpolateFn(scope);
+                  return;
+                }
+
                 var $$observers = (attr.$$observers || (attr.$$observers = createMap()));
 
                 // If the attribute has changed since last $interpolate()ed
@@ -4300,3 +4306,8 @@ function removeComments(jqNodes) {
   }
   return jqNodes;
 }
+
+
+function isConstantInterpolation(interpolateFn) {
+  return interpolateFn && interpolateFn.expressions.length === 0;
+}

test/ng/compileSpec.js

@@ -3577,6 +3577,15 @@ describe('$compile', function() {
       })
     );
 
+    it('should support non-interpolated `src` and `data-src` on the same element',
+      inject(function($rootScope, $compile) {
+        const element = $compile('<img src="abc" data-src="123">')($rootScope);
+        expect(element.attr('src')).toEqual('abc');
+        expect(element.attr('data-src')).toEqual('123');
+        $rootScope.$digest();
+        expect(element.attr('src')).toEqual('abc');
+        expect(element.attr('data-src')).toEqual('123');
+    }));
 
     it('should call observer only when the attribute value changes', function() {
       module(function() {