Preserve ThisBinding in conditionals & collapse_vars

Fixes #973

test/compress/issue-782.js

@@ -5,19 +5,19 @@ remove_redundant_sequence_items: {
         (0, 1, _decorators.logThis)();
     }
     expect: {
-        (0, logThis)();
+        logThis();
         (0, _decorators.logThis)();
     }
 }
 
-dont_remove_lexical_binding_sequence: {
+dont_remove_this_binding_sequence: {
     options = { side_effects: true };
     input: {
         (0, logThis)();
         (0, _decorators.logThis)();
     }
     expect: {
-        (0, logThis)();
+        logThis();
         (0, _decorators.logThis)();
     }
 }

test/compress/issue-973.js

@@ -0,0 +1,52 @@
+this_binding_conditionals: {
+    options = {
+        conditionals: true,
+        evaluate    : true
+    };
+    input: {
+        (1 && a)();
+        (0 || a)();
+        (0 || 1 && a)();
+        (1 ? a : 0)();
+
+        (1 && a.b)();
+        (0 || a.b)();
+        (0 || 1 && a.b)();
+        (1 ? a.b : 0)();
+
+        (1 && a[b])();
+        (0 || a[b])();
+        (0 || 1 && a[b])();
+        (1 ? a[b] : 0)();
+    }
+    expect: {
+        a();
+        a();
+        a();
+        a();
+
+        (0, a.b)();
+        (0, a.b)();
+        (0, a.b)();
+        (0, a.b)();
+
+        (0, a[b])();
+        (0, a[b])();
+        (0, a[b])();
+        (0, a[b])();
+    }
+}
+
+this_binding_collapse_vars: {
+    options = {
+        collapse_vars: true,
+    };
+    input: {
+        var c = a; c();
+        var d = a.b; d();
+    }
+    expect: {
+        a();
+        (0, a.b)();
+    }
+}