Revert r245843 content: Copy plugin code from Blink to Chromium.

Broke check_licenses, e.g. http://build.chromium.org/p/chromium.linux/builders/Android%20Builder%20%28dbg%29/builds/50681/steps/check_licenses/logs/stdio

> /b/build/slave/Android_Builder__dbg_/build/src/android_webview/tools/webview_licenses.py scan
The following files contain a third-party license but are not in a listed third-party directory and are not whitelisted. You must add the following files to the whitelist.
content/shell/tools/plugin/PluginObject.cpp
content/shell/tools/plugin/PluginObject.h
content/shell/tools/plugin/PluginObjectMac.mm
content/shell/tools/plugin/PluginTest.cpp
content/shell/tools/plugin/PluginTest.h
content/shell/tools/plugin/TestObject.cpp
content/shell/tools/plugin/TestObject.h
content/shell/tools/plugin/Tests/DocumentOpenInDestroyStream.cpp
content/shell/tools/plugin/Tests/EvaluateJSAfterRemovingPluginElement.cpp
content/shell/tools/plugin/Tests/EvaluateJSWithinNPP_New.cpp
content/shell/tools/plugin/Tests/FormValue.cpp
content/shell/tools/plugin/Tests/GetURLNotifyWithURLThatFailsToLoad.cpp
content/shell/tools/plugin/Tests/GetURLWithJavaScriptURL.cpp
content/shell/tools/plugin/Tests/GetURLWithJavaScriptURLDestroyingPlugin.cpp
content/shell/tools/plugin/Tests/GetUserAgentWithNullNPPFromNPPNew.cpp
content/shell/tools/plugin/Tests/InvokeDestroysPluginWithinNPP_New.cpp
content/shell/tools/plugin/Tests/LeakWindowScriptableObject.cpp
content/shell/tools/plugin/Tests/LogNPPSetWindow.cpp
content/shell/tools/plugin/Tests/NPDeallocateCalledBeforeNPShutdown.cpp
content/shell/tools/plugin/Tests/NPPNewFails.cpp
content/shell/tools/plugin/Tests/NPPSetWindowCalledDuringDestruction.cpp
content/shell/tools/plugin/Tests/NPRuntimeCallsWithNullNPP.cpp
content/shell/tools/plugin/Tests/NPRuntimeObjectFromDestroyedPlugin.cpp
content/shell/tools/plugin/Tests/NPRuntimeRemoveProperty.cpp
content/shell/tools/plugin/Tests/NullNPPGetValuePointer.cpp
content/shell/tools/plugin/Tests/PassDifferentNPPStruct.cpp
content/shell/tools/plugin/Tests/PluginScriptableNPObjectInvokeDefault.cpp
content/shell/tools/plugin/Tests/PluginScriptableObjectOverridesAllProperties.cpp
content/shell/tools/plugin/Tests/SlowNPPNew.cpp
content/shell/tools/plugin/main.cpp
< /b/build/slave/Android_Builder__dbg_/build/src/android_webview/tools/webview_licenses.py scan

BUG=331302
TBR=tfarina@chromium.org

Review URL: https://codereview.chromium.org/132053004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@245848 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 245848