Avoid uninitialized value warning in MemorySanitizer.

BUG=470391

Review URL: https://codereview.chromium.org/1090033002

Cr-Commit-Position: refs/heads/master@{#325519}

content/shell/renderer/test_runner/web_ax_object_proxy.cc

@@ -1168,7 +1168,7 @@ int WebAXObjectProxy::WordStart(int character_index) {
   if (accessibility_object_.role() != blink::WebAXRoleStaticText)
     return -1;
 
-  int word_start, word_end;
+  int word_start = 0, word_end = 0;
   GetBoundariesForOneWord(accessibility_object_, character_index,
                           word_start, word_end);
   return word_start;
@@ -1179,7 +1179,7 @@ int WebAXObjectProxy::WordEnd(int character_index) {
   if (accessibility_object_.role() != blink::WebAXRoleStaticText)
     return -1;
 
-  int word_start, word_end;
+  int word_start = 0, word_end = 0;
   GetBoundariesForOneWord(accessibility_object_, character_index,
                           word_start, word_end);
   return word_end;