Fix renderer crash and resulting test hang in PDFBrowserTests.
Fix renderer crash and resulting test hang in PDFBrowserTests.

I had assumed that didReceiveData() would only be called after Open(), but WebPluginImpl::didReceiveResponse() creates a PPB_URLLoader_Impl and immediately calls didReceiveData(). This correctly handles this case.

BUG=80684
TEST=PDFBrowserTest
TBR=brettw@chromium.org

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@84204 0039d316-1c4b-4281-b951-d872f2087c98

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