Surface page performance information in page info.

This is controlled via the PageInfoPerformanceHints feature, which is off by default.

This piggybacks on the PerformanceInfoObserver, which uses Cacao to fetch performance information for the current page. See https://docs.google.com/document/d/1YEPX-86zWtJ7JlFd_R4aGEybmMVbBltdXxF3T1RlYhI/edit for more information.

Screenshot: https://drive.google.com/open?id=1C1PvoKmjLkI-1Nr_QYg8AC-62B4RiY0R
Bug: 1076111
Change-Id: I329fca64a5a50b34a6daa54b44084fd68f275501
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2153889
Commit-Queue: Josh Simmons <[email protected]>
Reviewed-by: Mugdha Lakhani <[email protected]>
Reviewed-by: Theresa  <[email protected]>
Reviewed-by: Christian Dullweber <[email protected]>
Reviewed-by: Balazs Engedy <[email protected]>
Reviewed-by: David Trainor <[email protected]>
Cr-Commit-Position: refs/heads/master@{#764327}
diff --git a/chrome/browser/flag_descriptions.h b/chrome/browser/flag_descriptions.h
index 6c66a9b..644f6cc 100644
--- a/chrome/browser/flag_descriptions.h
+++ b/chrome/browser/flag_descriptions.h
@@ -1485,6 +1485,9 @@
 extern const char kOffliningRecentPagesName[];
 extern const char kOffliningRecentPagesDescription[];
 
+extern const char kPageInfoPerformanceHintsName[];
+extern const char kPageInfoPerformanceHintsDescription[];
+
 extern const char kPasswordManagerOnboardingAndroidName[];
 extern const char kPasswordManagerOnboardingAndroidDescription[];