Remove dead code in gr-textarea

The backgroundColor prop was unused in the app. This change removes it,
and sets inputs in the app to inherit their color instead of being the
default white.

Change-Id: Iaff2ae945f6a8e65739a66ec936002d80f21bb21

polygerrit-ui/app/elements/shared/gr-textarea/gr-textarea.html

@@ -41,7 +41,6 @@ limitations under the License.
         display: inline-block
       }
       #textarea {
-        background-color: var(--background-color, none);
         width: 100%;
       }
       #hiddenText #emojiSuggestions {

polygerrit-ui/app/elements/shared/gr-textarea/gr-textarea.js

@@ -70,10 +70,6 @@
         notify: true,
         observer: '_handleTextChanged',
       },
-      backgroundColor: {
-        type: String,
-        value: '#fff',
-      },
       hideBorder: {
         type: Boolean,
         value: false,
@@ -123,9 +119,6 @@
       if (this.hideBorder) {
         this.$.textarea.classList.add('noBorder');
       }
-      if (this.backgroundColor) {
-        this.updateStyles({'--background-color': this.backgroundColor});
-      }
     },
 
     closeDropdown() {

polygerrit-ui/app/elements/shared/gr-textarea/gr-textarea_test.html

@@ -25,7 +25,6 @@ limitations under the License.
 <link rel="import" href="gr-textarea.html">
 
 <script>void(0);</script>
-
 <test-fixture id="basic">
   <template>
     <gr-textarea></gr-textarea>
@@ -60,15 +59,6 @@ limitations under the License.
       assert.isTrue(element.$.textarea.classList.contains('noBorder'));
     });
 
-    test('background color is set properly', () => {
-      assert.equal(getComputedStyle(element.$.textarea).backgroundColor,
-          'rgb(255, 255, 255)');
-      element.backgroundColor = 'pink';
-      element.ready();
-      assert.equal(getComputedStyle(element.$.textarea).backgroundColor,
-          'rgb(255, 192, 203)');
-    });
-
     test('emoji selector is not open with the textarea lacks focus', () => {
       element.$.textarea.selectionStart = 1;
       element.$.textarea.selectionEnd = 1;

polygerrit-ui/app/styles/shared-styles.html

@@ -35,6 +35,7 @@ limitations under the License.
       }
       input,
       iron-autogrow-textarea {
+        background-color: inherit;
         box-sizing: border-box;
         margin: 0;
         padding: 0;