This is a simple move of ExtensionContext creation logic to
ExtensionChild.
Before the change, ExtensionContext was initialized as follows:
1. (ext-backgroundPage.js) Create background page
2. (Extension.jsm) document-element-inserted observed.
3. (Extension.jsm) new ExtensionContext + unload observer.
After this commit:
1. (ext-backgroundPage.js) Create background page
2. (ext-backgroundPage.js) emit extension-browser-inserted event
3. (Extension.jsm) Pass global to ExtensionContent + unload listener.
4. (ExtensionContent.jsm) document-element-inserted observed.
5. (ExtensionChild.jsm) new ExtensionContext
The next step is to use frame scripts and synchronize state.
MozReview-Commit-ID: K6mPdq7KQ2T
19ac7136a0
