Correctly whitelist the PDF plugin in the PDF extension.

Correctly whitelist the PDF plugin in the PDF extension.

For plugins listed in
chrome/browser/resources/plugin_metadata/plugins_*.json, the resource
identifier for that plugin becomes the key used in those JSON files.
Previously, the PDF plugin filename was used as the resource identifier
to whitelist the PDF plugin within the PDF extension. This caused the
whitelisting to be ineffective for official builds and also other builds
after r316957 added an entry for the Chromium PDF Viewer plugin. This CL
fixes this by using the keys from the plugin metadata files as the
resource identifiers for whitelisting the PDF plugin.

BUG=459998
Review URL: https://codereview.chromium.org/946293002

Cr-Commit-Position: refs/heads/master@{#317556}
(cherry picked from commit 2c8ef923fc3a440aa99b09372fde8f3d0893f551)

TBR=raymes@chromium.org

Committed: https://chromium.googlesource.com/chromium/src/+/41d95e3d4adb034a9f453f5b7f7100ee3de84c30

[Sam McNally, 2015-02-26 02:01:26]

sammc@chromium.org changed reviewers:
+ raymes@chromium.org

[Sam McNally, 2015-02-26 02:04:47]

Committed patchset #1 (id:1) manually as
41d95e3d4adb034a9f453f5b7f7100ee3de84c30 (presubmit successful).