DevTools: popover, selection and other minor theme tweaks.

third_party/WebKit/Source/devtools/front_end/popover.css

Index: third_party/WebKit/Source/devtools/front_end/popover.css
diff --git a/third_party/WebKit/Source/devtools/front_end/popover.css b/third_party/WebKit/Source/devtools/front_end/popover.css
index 8ff2496594d2690f07a5fea12458fc8cdf849da4..ef0064c4194cc2f2426213a726e82113d85181ad 100644
--- a/third_party/WebKit/Source/devtools/front_end/popover.css
+++ b/third_party/WebKit/Source/devtools/front_end/popover.css
@@ -37,6 +37,10 @@
     left: 0;
 }
 
+.-theme-with-dark-background .popover .arrow {
+    -webkit-filter: invert(80%);
+}
+
 .popover.top-left-arrow .arrow {
     /* The default is top-left, no styles needed. */
 }