[On-device adaptive brightness] Remove trailing whitespace.

This cl removes white space when we read ALS path and spec from command line.

Bug: 881215
Change-Id: I8a7373439793d0d3cd697c41ae882bbb10e7b455
Reviewed-on: https://chromium-review.googlesource.com/c/1328543
Commit-Queue: Jia Meng <jiameng@chromium.org>
Reviewed-by: Dan Erat <derat@chromium.org>
Cr-Commit-Position: refs/heads/master@{#606765}

chrome/browser/chromeos/power/auto_screen_brightness/als_reader_impl.cc

@@ -60,7 +60,7 @@ bool VerifyAlsConfig() {
   }
 
   const std::vector<base::StringPiece> num_steps = base::SplitStringPiece(
-      output, "\n", base::TRIM_WHITESPACE, base::SPLIT_WANT_ALL);
+      output, "\n", base::TRIM_WHITESPACE, base::SPLIT_WANT_NONEMPTY);
   return num_steps.size() == 7;
 }
 
@@ -80,6 +80,8 @@ std::string GetAlsPath() {
     return "";
   }
 
+  base::TrimWhitespaceASCII(output, base::TRIM_ALL, &output);
+
   if (exit_code != 0 || output.empty()) {
     LOG(ERROR) << "Missing ambient light path";
     return "";