DevTools: Remove vertical padding on text button

The text button has a fixed height, so it doesn't need vertical padding.
The padding caused the text to be not centered on Windows.

BUG=none

Review-Url: https://codereview.chromium.org/2938663002
Cr-Commit-Position: refs/heads/master@{#485134}

third_party/WebKit/Source/devtools/front_end/ui/textButton.css

@@ -10,7 +10,7 @@
     font-size: 12px;
     border: 1px solid rgba(0, 0, 0, 0.2);
     border-radius: 2px;
-    padding: 3px 12px;
+    padding: 0px 12px;
     font-weight: 500;
     color: #333;
     background-color: #fff;