Fix cause of uninitialized memory read in ExtensionService unit_tests

Fix cause of uninitialized memory read in ExtensionService unit_tests

In crrev.com/113111 I checked in code that reads a app state boolean from an 
ExtensionSyncData object which is uninitialized. This fixes the initialization
for the relevant constructor, and also limits reading that value to only when
the extension is an app.

BUG=106549
TEST=valgrind run of ExtensionService sync-related unit_tests should come back
clean

Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=113926

[asargent_no_longer_on_chrome, 2011-12-09 22:52:50]

For your reviewing pleasure...

[Matt Perry, 2011-12-09 23:05:59]

lgtm

[commit-bot: I haz the power, 2011-12-10 00:00:32]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/asargent@chromium.org/8899010/6

[commit-bot: I haz the power, 2011-12-10 02:31:26]

Change committed as 113926