Fix resource_sizes.py breaking if CWD!=src

BUG=678338

Review-Url: https://codereview.chromium.org/2761883002
Cr-Original-Commit-Position: refs/heads/master@{#458160}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 5664563554b429cc617b0ea8ebdd77293852492e

android/BUILD.gn

@@ -52,7 +52,8 @@ if (enable_java_templates) {
   _data +=
       "android_sdk_root=" + rebase_path(android_sdk_root, root_build_dir) + CR
   _data += "android_sdk_version=$android_sdk_version$CR"
-  _data += "android_tool_prefix=$android_tool_prefix"
+  _data += "android_tool_prefix=" +
+           rebase_path(android_tool_prefix, root_build_dir) + CR
   write_file("$root_build_dir/build_vars.txt", _data)
 }
 

android/resource_sizes.py

@@ -723,7 +723,8 @@ def main():
     constants.CheckOutputDirectory()
     devil_chromium.Initialize()
     build_vars = _ReadBuildVars(constants.GetOutDirectory())
-    tools_prefix = build_vars['android_tool_prefix']
+    tools_prefix = os.path.join(constants.GetOutDirectory(),
+                                build_vars['android_tool_prefix'])
   else:
     tools_prefix = ''