Fixes a bug that could occur while a user searches in a plugin document if the plugin is no longer present. Since an extension could remove the plugin object from the page and replace it with HTML content, a user may then want to search through the HTML content.  This currently causes a segmentation fault since the plugin no longer exists.  This patch adds an extra check to make sure that the plugin still exists before it is used.
Fixes a bug that could occur while a user searches in a plugin document if the plugin is no longer present.
Since an extension could remove the plugin object from the page and replace it with HTML content, a user may then want to search through the HTML content.  This currently causes a segmentation fault since the plugin no longer exists.  This patch adds an extra check to make sure that the plugin still exists before it is used.

Review URL: http://codereview.chromium.org/7211024

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@90144 0039d316-1c4b-4281-b951-d872f2087c98

gavinp/chromium,gavinp/chromium,adobe/chromium,adobe/chromium,yitian134/chromium,yitian134/chromium,adobe/chromium,gavinp/chromium,adobe/chromium,adobe/chromium,adobe/chromium,gavinp/chromium,yitian134/chromium,gavinp/chromium,yitian134/chromium,yitian134/chromium,yitian134/chromium,ropik/chromium,ropik/chromium,gavinp/chromium,yitian134/chromium,adobe/chromium,ropik/chromium,adobe/chromium,ropik/chromium,gavinp/chromium,adobe/chromium,gavinp/chromium,ropik/chromium,adobe/chromium,ropik/chromium,gavinp/chromium,adobe/chromium,ropik/chromium,ropik/chromium,yitian134/chromium,yitian134/chromium,yitian134/chromium,gavinp/chromium,ropik/chromium