Fix crash when loading unreachable image

Also fixes crashes that happen when using Saved Pages with
images that are not in the WebView cache

Bug: 63890
Change-Id: Ia1b0f534b0c07c0fd584db31c4354d67ed703576
Moved search handler to its own class

Change-Id: I4be491bcf6ad7a6161e5e767f4022737939aa1c5