Clean up histogram'd media enum max values.

This adds a PRESUBMIT test to src/media/ which enforces the following when using UMA_HISTOGRAM_ENUMERATION:
- The max enum value should be suffixed with 'MAX' or 'Max' (and it should be equal to the largest valid entry ever logged).
- One should be added to that max value when used in the UMA_HISTOGRAM_ENUMERATION macro.

To handle past misuses of UMA_HISTOGRAM_ENUMERATION for non-enums a comment of '// IGNORE_PRESUBMIT_UMA_MAX' was added to silence the presubmit check.

BUG=165553
TBR=danakj

Review URL: https://codereview.chromium.org/148553003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@254209 0039d316-1c4b-4281-b951-d872f2087c98
Ensure the pending entry is not deleted during NavigateToEntry.

Also makes NavigateToEntry private in favor of NavigateToPendingEntry, since we should only get to the former via the latter.

BUG=347742
TEST=CHECKs instead of memory errors for the cases on the bug.

Review URL: https://codereview.chromium.org/181013005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@254210 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 254209
SVN changes up to revision 254210